toolboy's Corner: Ryobi 40v Charger Testing

Note: Additional testing results can be found here: Ryobi 40v Charger Testing #2

Ryobi's 40v tool offerings are becoming quite expansive. I've purchased and regularly use a number of these 40v tools. I started with an attachment-capable power head and a leaf blower. All of the attachments I had already purchased for my gas-powered Troybilt TB575SS power head were 100% compatible with the 40v power head: a string trimmer, a brush cutter, a pole saw, an articulating hedge trimmer, and a cultivator. I soon purchased a 40v chainsaw, and I eventually picked up a lawn mower and a 300w pure sine wave AC inverter. These are all great tools! But I soon found that it can be difficult to stay busy, because once a battery has been depleted it takes several hours to recharge. This is especially true if other family members are mowing and/or string trimming the lawn while I'm working on something else. That's three batteries in use at once.

At the start of this testing, my arsenal of 40v batteries included one 5Ah battery, two 4Ah batteries, and one 2.6Ah battery. I've since added a couple of 6Ah batteries (model OP40601 - the original model with the short profile). If these are all drained and only one charger is available, it'll take a full day to recharge them all. It's really ridiculous that Ryobi has only recently released a rapid charger for these batteries. The cells inside these battery packs are designed to be recharged at the 1C rate. This means that, in theory, the cells should be able to go from completely discharged to fully charged in exactly one hour without exceeding the cell manufacturer's recommendations. Due to the way a modern CC/CV charger operates and how Li-Ion cells accept a charge, my expectation is that an additional 25-30% in time will be needed to keep the cells from overheating as they near a full charge. Let's call it 75 minutes or 01:15. If the charger takes much longer than this, then it's just wasting our time without adding any safety.

Are Ryobi's 40v batteries really 40v?

If you're familiar with Ryobi's ONE+ line of 18v tools, you might know that the 18v Li-Ion batteries contain five 18650 cells in series. Each 18650 cell has a nominal voltage rating of 3.6v, so five in series yields 5x3.6v= 18v. The claimed 40v can't be divided equally with 3.6v cells, so something is awry. It seems far more likely that Ryobi simply doubled the number of cells from their 18v batteries, or ten cells in series. That would mean the 40v batteries are really 10x3.6v = 36v. I've disassembled several 40v batteries and I can confirm that they contain ten cells in series (or two parallel strings of ten cells) so yes, they're really 36v batteries.

What does a "1C" charge rate mean?

Often you will see a number followed by a capital "C" to describe a charge rate. This is a measure of rate relative to the capacity measurement of the cell. So "1C" means that a cell can be charged at a rate (in amps) which is the same as the cell capacity (in amp hours). The 1C charge rate for a cell rated 1.5Ah would be 1.5A, and for a 3Ah cell the 1C rate would be 3A. In theory, if a depleted cell is charged at a 1C rate it will reach a full charge in one hour. If charged at the 2C rate it will reach a full charge in 1/2 hour, and if charged at the 10C rate it will reach a full charge in 1/10th hour (=6 minutes!) In reality, the charge times will take longer because the charge rate must typically be decreased as a cell reaches full charge to avoid damaging the cell.

What is a CC/CV charger?

The "CC" in "CC/CV" stands for "Constant Current" and the "CV" stands for "Constant Voltage". This term describes a 2-stage charger which delivers a constant current to recharge a battery until the battery reaches a certain level, then the charger decreases the charge rate and continues to decrease the charge rate until the battery has reached a full charge. For example, a charger may deliver 4A to recharge a deleted 6Ah battery for 75 minutes, then it decreases the charge rate to 3A for 5 minutes, then every 5 minutes the charge rate is decreased by 0.5A until the charge rate reaches 0.5A, then the charger stops when battery reaches a full charge. (This example is an oversimplification, often the CV stage is much more of a curve than described here.)

Do the Ryobi 40v battery models mean anything?

Yes, the battery model numbers indicate battery capacity. Each battery model begins with "OP40" to indicate the 40v battery line. The next two digits indicate the battery capacity in Ah x10 (e.g., 15 = 1.5Ah, 40 = 4.0Ah, etc.) The model may have an additional digit, which I presume indicate revision number. So the 1.5Ah battery is model OP4015, the 2.6Ah battery is OP4026 or OP40261, the 4.0Ah battery is OP40401, and the 7.5Ah battery is OP40751.

My 40v battery contains TWO strings of 10 cells. Shouldn't it be possible to recharge it safely in half the time, or 30 minutes?

No, it doesn't work that way. To stay within the manufacturer recommend charge rate of 1C the fastest that any individual cell can be charged is 1C or in one hour, regardless of how cells are wired within the battery pack. Ryobi has released 40v batteries containing ten, twenty, or thirty 18650 Li-Ion cells. These cells are wired as 10S1P, 10S2P, or 10S3P, which means that they are wired with ten cells in series and then 1, 2, or 3 sets of ten wired in parallel. Ryobi has released (or announced) 40v batteries in the following capacities/configurations:
Capacity (Ah)Model(s)Cell ConfigurationCapacity per cell (Ah)Cells(s) UsedSpecs
1.5 OP4015 10S1P 1.5AhLG HB2 1500mAh,30A,3.65v
2.0 OP40201 10S1P 2.0AhLG HD2?  
2.6 OP4026, OP40261 10S2P 1.3AhLG HA1
Samsung INR18650-13
1300mAh, 15A, 3.68v
1300mAh, ??A, ??v
3.0 OP4030, OP40301 10S2P 1.5AhSamsung 15Q?  
4.0 OP4040, OP40401 10S2P 2.0AhLG HD2?  
5.0 OP4050, OP40501 10S2P 2.5AhLG HE2?  
6.0 OP40601 10S2P 3.0AhLG HG2?  
6.0 OP40602 10S3P 2.0AhLG HD2?  
7.5 OP40752 10S3P 2.5AhLG HE2?  
8.0 OP4080 ??? ???Ah???  
9.0 OP40902 ??? ???Ah???  
12.0 OP4012A1 ??? ???Ah???  

Given that Ryobi has used twenty 3.0Ah cells in the original 6.0Ah battery and thirty 2.5Ah cells in the 7.5Ah battery, I expect that at some point Ryobi will release a 9.0Ah battery containing thirty 3.0Ah cells which would be about the same size as the 7.5Ah battery. On the other hand maybe not, given that Ryobi changed the 6Ah battery from twenty 3.0Ah cells to thirty 2.0Ah cells sometime in 2020. I don't know why they made this change (perhaps is was simply economics) but I don't much care for it as the larger battery size cannot be used with certain tools such as the chainsaw.

Update 25-Jun-2021: Ryobi has not actually changed the 6.0Ah battery from 20 cells to 30 cells, they're still manufacturing and selling both the 20-cell OP40601 and the 30-cell OP40602. I think they did this purposefully and because the 30-cell battery can probably better sustain a heavy load than a 20-cell battery. This probably doesn't matter much for most tools, but consider the RYi1802B6 inverter which is rated 1800W running. With an estimated 12% overhead for DC-AC conversion, that means the battery (or batteries) must supply (1800W)*(1.12)= 2016W in order to maintain that output level. The operating voltage range for a battery is about 42v-30v, which means that the battery must deliver from 2016W/42v=48A to 2016W/30v=67A. I haven't cracked open an OP40601 or OP40602 battery to verify the actual cells used, but based on the fact that Ryobi has used only LG and Samsung cells in all of the batteries I've opened and looking at the cells that these manufacturers offer, it's reasonably safe to think that the cells in these batteries are rated for 20A continuous output. Therefore, the maximum sustained current that a single 30-cell Ryobi battery can deliver is 20A*3=60A and the maximum sustained current for a 20-cell battery is 20A*2=40A. So a single battery with 20 cells cannot sustain a 48A-67A load at all. A 30-cell battery can theoretically deliver the required energy when at a full charge but as the battery discharges the current required will eventually exceed the cell's sustained current ratings before the battery is fully discharged. No doubt this is why Ryobi includes two of the taller/larger 30-cell OP40602 batteries in the RYi1802B6 Inverter Kit rather than the shorter/smaller 20-cell OP40601 batteries.

Sadly, the 40v batteries don't communicate with the charger to indicate what the maximum charge rate should be or how many strings of cells are present in 40v battery. So each 40v charger operates at the same charge rate irrespective of which battery has been selected. This works well for batteries containing ten cells (10S1P), but means that the charge times are 2x or 3x longer than they need to be for twenty cell (10S2P) and thirty cell (10S3P) batteries.

The Ryobi 40v batteries have SEVEN contacts, but only THREE are used for charging, and only FOUR are even wired. Hey Ryobi, why not use one or more of the three unused contacts to tell your chargers how fast they can charge the battery? For example, strap a contact to +Vcc to indicate TRUE or 1, to Ground or no contact for FALSE or 0. An old battery without these strappings would be 000. Then if we have a multi-level current charger, let bit 1 indicate increased rate, bit 2 = double rate, bit 3 = triple rate. For example: Perhaps the last two combinations should be illegal. At any rate, if we strap bit 2 or 3 to indicate a 10S2P or 10S3P cell configuration we safely cut the charge time in half or a third, respectively.

Is it dangerous to charge a battery at a rate exceeding the cell manufacturer's recommended maximum charge rate?

That all depends on how greatly the recommended maximum rate is exceeded. Cell manufacturers test their cells and then select a maximum charge rate which meets their criteria for safety and marketing.

The safety aspect is obvious. If the recommended maximum charge rate is too high, cells are likely to rupture or start a fire, causing damage or injury (and costly litigation).

The marketing aspect is less obvious. The higher the charge rate, the sooner the cells are fully charged. Consumers always want the fastest charge time. But higher charge rates also mean decreased cell longevity. Consumers also want cells that will last for as many cycles as possible. Manufacturers select a maximum charge rate which will allow them to claim that the cell is good for a certain number of charge cycles. A given cell may be rated for a 1C charge rate and 300 charge cycles. That same cell could probably be charged at the 2C rate, but in so doing the number of expected charge cycles might be decreased to 150. Charging that same cell at a 0.5C rate might increase the number of expected cycles to 500. Would a consumer prefer to cut their charge time in half at the expense of reducing the number of charge cycles in half? That's a marketing call. (Incidentally, these numbers are just guesses, I don't have any insight into the real numbers manufacturers are working with.)

I wouldn't recommend charging a cell at more than twice a manufacturer's recommended maximum charge rate, but that's just my opinion. I have no hard data to support this recommendation. Cell temperatures should be monitored during charging no matter what rate is selected. This is especially true when the manufacturer recommended maximum charge rate is exceeded. If the cells become too warm, stop the charge cycle and let them cool before proceeding!

Some questions I'll try to answer on this page:

How long does it take to recharge a 40v battery on a 40v charger?

This is not a simple question with a simple answer.

Ryobi has released 40v batteries in capacities which range from 1.5Ah to 7.5Ah. Unless the Ryobi 40v chargers adjust their charge rate to fit the battery which is being charged it is reasonable to expect that it will take 5x as long to recharge a 7.5Ah battery as compared to a 1.5Ah battery on a given model of charger, since the 7.5Ah battery has 5x the capacity of the 1.5Ah battery. If it takes one hour to recharge a 1.5Ah battery, we should expect that it will take 5 hours to recharge a 7.5Ah battery on the same charger. So we can't really say how long it will take to recharge a battery without first knowing WHICH battery.

Ryobi has released at least SIX different models of 40v chargers. Do they all operate at the same charge rate? In order to recharge a 1.5Ah battery in exactly one hour, a charger must be delivering an average charge rate of at least 1.5A. (And the actual charge rate will be a little bit higher to account for energy losses due to heat and other factors.) If the charge rate of another charger model is 2.0A, then we should expect the 1.5Ah battery recharge time to be 1.5Ah/2A = 0.75hr, or 45 minutes. The second charger model is therefore 15 minutes faster than the first model for the 1.5Ah battery! Most consumers will not be sitting by with a stopwatch so this difference may go unnoticed. If we apply this same logic to the 7.5Ah battery, we see the charge time would be 7.5Ah/1.5A = 5 hours vs 7.5Ah/2A = 3.75 hours. That's an hour and fifteen minutes faster on the second charger, which may be long enough for many consumers to notice. So we can't really say how long it will take to recharge a battery without first knowing WHICH charger.

Here is the list of 40v chargers which Ryobi has released (or announced) in the USA: I happen to own at least one of each of these models up to the P407. I plan to test each of them except for the OP404 (which I can't imagine would operate any differently than the OP403).

I've selected a 4Ah battery for all of the testing. The 4Ah battery is in the middle of the range of available capacities, and it's the battery Ryobi is bundling with most of their $100-$200 tool kits. The actual battery I have for testing has a date code indicating it's age is 66 weeks or about 1 year and 3 months.

In the testing below, I'm reporting a number of values. Here's a definition of what I mean by these terms.

Ryobi 40v OP400 Charger

This model has been discontinued by Ryobi. Early reviewers of this charger reported that it was responsible for killing their battery. As I understand it, Ryobi offered replacement batteries and chargers to many consumers who complained. I've charged many 40v batteries on OP400 chargers (mostly the 2.6A batteries) and I've never had a problem. This label on this charger indicates that it's rated 88W input.

4Ah OP40401 Battery on Ryobi OP400 Charger

Charger OP400 (88W)
Battery OP40401 (rated 4Ah / 144Wh)
Total Charge Time 2:23:23 (8,603 sec)
Current In 3.8755A
"Bulk" charge rate 1.73A
Average charge rate1.638A
Measured Capacity 3.751Ah / 137.02Wh

The graph shows that the OP400 is a typical CC/CV charger.

Ryobi 40v OP401 Charger

This model replaced the older OP400. It has a slightly smaller footprint than the older OP400, and it's not nearly as tall. The OP401 is rated 72W input so I expect a lower charge rate and longer charge time than the OP400.

4Ah OP40401 Battery on Ryobi OP401 Charger

Charger OP401 (72W)
Battery OP40401 (rated 4Ah / 144Wh)
Total Charge Time 3:13:37 (11,617 sec)
Current In 3.9156A
"Bulk" charge rate 1.28A
Average charge rate1.221A
Measured Capacity 3.569Ah / 129.44Wh

Once again we see the curve of a typical CC/CV charger. As expected, this is a lower charge rate and a longer charge time than the OP400.

Ryobi 40v OP403 Charger

The OP403 charger is very small compared to the OP400 and OP401. It consists of two parts, one part which attaches to the 40v battery and a "wall wart" on the other end which plugs into your household AC outlet. The part which attaches to the battery is similar to an oversized bar of soap. The OP403 has an indentation in one corner with a USB port providing 5v at up to 2.1A. This can be used for charging cell phones or with other USB-powered devices. The USB port can be powered by the "wall wart" AC adapter or by the battery alone, making it useful as a power source during power outages or while camping, etc. The "wall wart" is rated 80W input, which puts this charger halfway between the OP400 and the OP401.

4Ah OP40401 Battery on Ryobi OP403 Charger

Charger OP403 (80W)
Battery OP40401 (rated 4Ah / 144Wh)
Total Charge Time 2:35:29 (9,329 sec)
Current In 3.7757A
"Bulk" charge rate 1.47A
Average charge rate1.467A
Measured Capacity 3.644Ah / 132.73Wh

I'm a little surprised to find that the OP403 is strictly a CC charger, not a CC/CV charger like the OP400 and OP401. The "bulk" and average charge rate are pretty much the same thing for a CC charger.

Ryobi 40v OP406A Rapid Charger

This charger is the beast. Ryobi claims "Up to 300% Faster Charging than Standard RYOBI 40-Volt Charger". Ryobi also claims that the charge time for a 2Ah battery is 30 mins, 4Ah/40 mins, 5Ah/50 mins, 6Ah/60 mins, and 7.5Ah/75 mins. The OP406A is rated a whopping 295W input.

4Ah OP40401 Battery on Ryobi OP406A Charger

Charger OP406A (295W)
Battery OP40401 (rated 4Ah / 144Wh)
Total Charge Time 0:48:40 (2,920 sec)
Current In 3.8508A
"Bulk" charge rate 6.15A
Average charge rate4.797A
Measured Capacity 3.060Ah / 109.42Wh
Wow! The OP406A is indeed a RAPID charger! It's a CC/CV charger with a bulk charge rate of 6.15A! The OP406A has an integrated fan which kicked in immediately when the charge cycle began. My 4.0Ah battery got very warm to the touch while charging. I'll mention this in case anyone isn't sure: HEAT = BAD when it comes to battery longevity. When I heard the fan cut off I looked over and saw that the green light was still flashing, as if to indicate that the charge cycle was ongoing. But my datalogger showed that no current was going in or out of the battery. I decided to leave everything alone for a while. Maybe the charger had detected that the battery was warm and wanted to let it cool off before declaring the charge cycle complete. If so, then do I include this cool down period in the total charge time I record for this charger? After watching the blinking green light for more than 45 minutes without a change in charge current (it remained zero) I stopped watching. 24 hours later the green light was still blinking, and after 36 hours I noticed the light was no longer blinking, it was just out. I find it curious that at 34:20 when the pack voltage reached 42v, the charge current dropped from 6.15A to 4.62A, where it remained until 35:35. The remainder of the curve was typical for a CV charger. The total charge time was about 48 minutes, which is very fast but about 20% longer than the advertised claim of 40 minutes for a 4Ah battery.

I did receive a surprise when I tested the battery capacity on the computerized battery tester. The battery tested at 3.06Ah / 109.42 Wh, or at about 76.5% of its rated capacity. That's really awful, given that this battery had tested between 89%-94% with all of the other chargers. Below is the graph which shows this. Can you guess which curve followed the OP406A charge cycle? Yup, it's the orange one.

One other thing that catches my attention in the curves above is that the tests did not really continue all the way to the lower limit of 28v as I'd configured them. Each of the curves takes a nose dive at 30v. This is the level where the battery's internal circuit disconnects the battery from the load to protect it from over-discharging. This is a good thing!

The OP406A's "bulk" charge rate of 6.15A actually exceeds the cell manufacturer's recommended maximum charge rate for most Ryobi 40v batteries. Here's why: As can be seen above, the charge rate of the OP406A charger exceeds the 1C rate for all Ryobi 40v batteries except for the 7.5A OP40751. OK, so the charge current of the OP406A just barely exceeds the 1C charge rate for the 6Ah OP40601/OP40602 (103% of 1C rate). This is probably OK.

I recommend using the OP406A sparingly or not at all on batteries under 6.0Ah in capacity.

Update 13-Jul-2020: I've now tried countless times to charge my 2.6A OP4026 40v battery on the OP406A without success. When I "click" the battery into the OP406A charger, the charger's fan winds up and the LEDs flash for a moment, then the fan stops and the LED flashes an alternating red/green as if the battery were defective. I've tried charging the OP4026 when fully depleted, when about 3/4 depleted, 1/2 depleted, and even when only about 1/4 depleted. The OP406A won't attempt to charge it. When this first happened I actually thought the charger was faulty and I was thinking of returning it. But then it successfully charged a 4A OP40401, so it seemed that the charger was OK. To repeat what was stated above: If you're considering the OP406A be certain that you plan to use it only with higher capacity batteries!

Ryobi 40v OP407 Charger

This model was released by Ryobi in Feb 2021, and I picked one up immediately. The box claims "2x Faster Charging [compared to OP403]", "1 Hour Charge Per Port", and "Compatible with all Ryobi 40 Batteries". We'll see. The OP403 is rated 80W and the OP407 is rated 194W, which is a little more than 2x the power.

4Ah OP40401 Battery on Ryobi OP407 Charger

Charger OP407 (194W)
Battery OP40401 (rated 4Ah / 144Wh)
Total Charge Time 1:07:21 (4,041 sec)
Current In 3.8177A
"Bulk" charge rate 4.05A
Average charge rate3.431A
Measured Capacity 3.703Ah / 134.70Wh (92.6%)

The 4Ah battery was warm to the touch when the charge cycle ended so I set it aside for an hour before I performed the capacity test. As mentioned above with the OP406 rapid charger: HEAT = BAD when it comes to battery longevity. As the measured charge rate is 4.05Ah I'll have to recommend that this charger be used ONLY with batteries with a rated capacity of 4Ah and larger. The OP403 took 9,329 seconds to charge the 4Ah battery and the OP407 to 4,041 seconds. So as it turns out, for a 4Ah battery the OP407 is actually 2.3x faster than then OP403, which exceeds Ryobi's claim of 2x!

The next battery I attempted to charge with the OP407 was a 2.6Ah OP40261. This battery charged with a bulk rate of 3.7A, which is LESS than the 4.05A rate which the 4Ah battery experienced. So it seems that the OP407 charger may have a variable charge rate which takes into account the capacity of the battery being charged! Wow!

Can we predict how long it takes to recharge a Ryobi 40v battery?

Maybe, but we must know WHICH battery and WHICH charger, and we must make some additional assumptions. I'm not going to go into great detail wrt the assumptions, more details can be seen on my web pages which discuss Ryobi 18v charger testing. I'll just state that my assumptions for the table below are that (1) each battery has been tested to be operating with the ACTUAL capacity as stated in the table, (2) each battery has been fully discharged before beginning the charge cycle, and (3) both battery and charger are at room temperature before starting and during the charge cycle. The table below lists actual recharge times that I've measured using a datalogger configured to capture 4 pts/sec. I'll add to this table as I gather more data.

Will the recharge times be the same with your battery/charger combo? Probably not. But if your battery's ACTUAL capacity is the same as the one I performed testing with, then the recharge times should be about the same. If your battery's ACTUAL capacity is greater than my test battery then recharge times will be longer. If your battery's ACTUAL capacity is less than my test battery then recharge times will be shorter.

Battery Model(s)Rated Capacity (Ah)ACTUAL Capacity (Ah)
/ % of Actual
Recharge Time on Charger Model
OP40601 6.0 5.515 / 92% 3:36:34
(12,994 sec)
(20,407 sec)
(13,921 sec)
(4,551 sec)
(5,977 sec)
OP40401 4.0 3.675 / 92% 2:23:23
(8,603 sec)
(11,617 sec)
(9,329 sec)
(2,920 sec)
(4,041 sec)
OP4026 2.6 2.305 / 89% 1:27:32
(5,252 sec)
(7,065 sec)
(5,609 sec)
N/A 0:48:57
(2,937 sec)

Can a Ryobi 40v charger be modified (safely) to work faster?

When I look at the OP403/OP404 40v charger I see two main components: a charger and a power supply. And the testing performed above shows that the OP403 is a CC only design. That got me thinking. Which component is responsible for limiting the charge current, the charger or the power supply? If it's the power supply, then can the charge rate be increased by replacing the power supply with a more powerful one? The OEM power supply is rated 80W in and 42V DC at 1.5A out. A quick check on eBay reveals many sellers of inexpensive power supplies rated for an output of 42V DC at 2.0A. If it works, that would be 33% faster than the OEM power supply.

Before buying anything I decided to do a proof of concept (POC) test. I looked though my supplies and parts bins and decided that I could test this concept by combining the power from two OEM power supplies. We can't just tie the outputs together as small manufacturing differences between the two would likely cause the one with the slightly higher voltage output to back feed into the other unit and possibly fry something. So instead I connected one directly to the OP403 charger, and the other I connected through a resistor. Actually I used two 10 Ohm 10W power resistors in parallel. I figured that the power supply with no resistor would supply a full 1.5A and the other one would kick in a little extra, perhaps as much as 0.5A. I did expect that the "extra" juice provided by the second power supply would decrease as the battery voltage increased.

4Ah OP40401 Battery on Ryobi OP403 Charger with extra power supply

Charger OP403 (80W + extra 80W power supply via 5 Ohm power resistor)
Battery OP40401 (rated 4Ah / 144Wh)
Total Charge Time 1:34:53 (5,693 sec)
Current In 3.7217A
"Bulk" charge rate 3.02A-1.62A
Average charge rate2.375A
Measured Capacity 3.354Ah / 120.98Wh
Firstly let me mention that the battery's actual capacity tested low. This is the first charge cycle following a charge on the monster OP406A, so I'm not certain if the problem is with this POC test or if the battery is still recovering from the wallop that the monster OP406A charger gave it. I may cycle it a few times on an OP401 (the slowest 40v charger) to see if it recovers, then try this POC again.

The 4Ah battery DID charge faster with the extra oomph, so I think it's the power supply which limits the current to the OP403 charger. The charge rate starts high and diminishes during the charge cycle, as expected. The charge rate starts at 3.02A and slowly drops during the entire charge cycle, ending at 1.62A. This is a positive result for the POC test, and I think it's worth purchasing a 42v 2A power supply to see how this works. I might even get a 2.5A unit if I can find one. I see that 3A and 4A power supplies are available, but I'm hesitant to get one of these because (1) they are substantially more expensive than the 2A models, and (2) the charger is actually sold with a 1.5A power supply, so the more power we use the more likely we are to exceed what the charger can handle and violate some internal component(s).

From the table above which lists all battery models in the OP406A section, we determine if a 2A, 2.5A, or 3A power supply would exceed the cell manufacturer's maximum charge rate for any of the Ryobi 40v batteries. I calculate that a 2A power supply would exceed the max rate for just the 1.5A OP4015 battery. A 2.5A unit would exceed the max rate for both the 1.5A OP4015 and the 2.0A OP40201 batteries. A 3A or 4A unit would exceed the max rate for the previous two plus the 2.6A OP4026 and OP4026A. I don't happen to own any 1.5Ah or 2.0Ah batteries and I don't plan to get any, so a 42v 2.5A power supply sounds perfect to me.

Would this be faster than an OP403 alone? Yes! Remember the OP403 took 2:35:29 to recharge the 4Ah battery, whereas in this POC test the recharge took only 1:34:53. This shaved a full hour from the charge time. That's (5693 sec)/(9329 sec) or 61% of the original time. The POC test averaged a 2.375A charge rate, so with a 2.5A power supply the charge time should be even faster.

Bear in mind that there is some risk with this approach. The charger was sold with and was probably designed to be used with a 42v 1.5A power supply. A larger power supply could potentially overheat the unit, causing permanent damage. The unit could even catch fire. You have been warned!

Several weeks after the preceding POC test I acquired a Mean Well HLG-185H-42B LED power supply. This unit is rated 42v DC at up to 4.4A (185W), and features adjustable output current (with the addition of a 100K Ohm potentiometer). I've adjusted the pot such that the OP403 delivers 2.5A while charging.

4.0Ah OP40401 Battery on Ryobi OP403 Charger with 2.5A power supply

Charger OP403 (2.5A power supply)
Battery OP40401 (rated 4Ah / 144Wh)
Total Charge Time 1:48:06 (6,486 sec)
Current In 3.7346A
"Bulk" charge rate 2.48A
Average charge rate2.09A
Measured Capacity 3.70Ah / 134.86Wh (92.5%)

Well that didn't quite go as planned. The curve isn't CC only, like when using the factory-supplied power supply. It's a CC/CV curve with 2.5A for 1 hour and 21 minutes (40.88v) then the current started tapering off. The charge cycle never actually ended. I disconnected the battery after having left this charger connected overnight. I've arbitrarily decided to define the "end of charge" as the point where the charge current first dropped to 0.25A, which more-or-less aligns with the end of charge cycle for the OP400, OP401, and OP406A.

I think the problem is that the output voltage from the Mean Well just isn't high enough, so the battery never reaches a "full charge". I've measured the no load voltage of the Mean Well at 42.3v and the Ryobi at 43.7v. I cracked open the Mean Well thinking that I might reverse engineer it just enough to boost the output a little, but discovered that the entire inside of this unit is potted! Oh well.

Obviously the OP403 unit can handle the higher charge current, and this still works as a fast charger if one monitors the output current and removes the battery when the charge current drops to 0.25A. Or maybe remove it when the last light on the battery starts blinking.

I tried again, and this time I set the Mean Well to output 3.5A. Every once in a while I glanced over at the datalogger and stopped the charge cycle when the current dropped to 0.25A.

4.0Ah OP40401 Battery on Ryobi OP403 Charger with 3.5A power supply

Charger OP403 (3.5A power supply)
Battery OP40401 (rated 4Ah / 144Wh)
Total Charge Time 1:26:05 (5,165 sec)
Current In 3.7399A
"Bulk" charge rate 3.49A
Average charge rate2.633A
Measured Capacity 3.638Ah / 132.43Wh (90.9%)

As expected, it's a CC/CV curve. And the OP403 survived, so it seems that the 3.5A power supply is not too much for it.

The Mean Well is rated for 185W, or 4.4A at 42v. So I'll try one last time with the current set at the maximum output level. Once again, I'll stop the test when the charge current has dropped to 0.25A.

4.0Ah OP40401 Battery on Ryobi OP403 Charger with 4.4A power supply

Charger OP403 (4.4A power supply)
Battery OP40401 (rated 4Ah / 144Wh)
Total Charge Time 1:17:23 (4,637 sec)
Current In 3.7671A
"Bulk" charge rate 4.25A
Average charge rate2.949A
Measured Capacity Ah / Wh (%)

I've now picked up a DC-DC Step-Up Adapter, rated for up to 600W. (See HERE.) I'm using an 18v@20A switching power supply as the power source, and I've adjusted the device to deliver 43.8v at about 4A. Hopefully this will keep the OP403 in its CC mode for the full charge cycle.

4.0Ah OP40401 Battery on Ryobi OP403 Charger with 43.8v@4.0A DC-DC Adapter

Charger OP403 (43.8v@4.0A DC-DC Adapter)
Battery OP40401 (rated 4Ah / 144Wh)
Total Charge Time 1:28:18 (5,298 sec)
Current In 3.8230A
"Bulk" charge rate 4.0A
Average charge rate2.621A
Measured Capacity 3.385Ah / 122.09Wh (84.6%)

The DC-DC adapter became very warm while charging. I picked it up off the table and slid another device with an aluminum chassis under it to help dissipate the heat. The OP403 also became quite warm, so a charge current of 4A may be about the upper limit for this device. Occasionally I monitored the charger current, input voltage, and battery voltage. I observed that the charger current did decrease slowly, as did the voltage differential I first recorded 4.0A and 38.00v Adapter vs. 35.70v Battery then after about 15 minutes it had dropped to 3.5A and 39.98v Adapter vs. 37.72v Battery, later I recorded 1.8A and 42.00v Adapter vs. 40.60v Battery. 41.77v 43.00v 0.91A

OK so it didn't stay in the CC mode for the full charge cycle. It kept the 4A going for about 12 minutes then began to decline. I'll keep fiddling and see what yields the best results. My goal is deliver a steady charge current (up to 4A) for at least 80% of the charge cycle.

On my next attempt I tweaked the DC-DC Adapter to output 44.5v, and I left the current adjustment alone (4.0A).

4.0Ah OP40401 Battery on Ryobi OP403 Charger with 44.5v@4.0A DC-DC Adapter

Charger OP403 (44.5v@4.0A DC-DC Adapter)
Battery OP40401 (rated 4Ah / 144Wh)
Total Charge Time 0:54:44 (3,284 sec)
Current In 3.6143A
"Bulk" charge rate 4.02A
Average charge rate4.005A
Measured Capacity 3.513Ah / 127.54Wh (87.8%)

While this test was running, I looked over and saw a little smoke rising over the DC-DC Adapter. I quickly put a muffin fan on it then sat back and watched it, a bit disappointed that a device rated for 600W couldn't handle 44.5v@4A = 178W. Then I saw more smoke rising, and realized that it wasn't the DC-DC Adapter that was smoking, it was my cheap jumper wires! I had not taken the time to connect everything with 12GA wires and 45A Anderson PowerPole connectors as I normally would, I had connected it all with jumper wires while testing. Big mistake. I quickly clipped a second set of heavier jumper wires in parallel with the first set and the original jumpers cooled down quickly. Now I'm wondering if my first test with the DC-DC Adapter was biased by the use of improperly gauged jumper wires.

This time I got the result I was hoping for! The curve shows a steady 4A for 52 minutes, then for two minutes the charge current decreases steadily down to 3.45A, at which point the charge cycle ends. The 4Ah battery has been fully recharged in under an hour with an OP403!

I did one more run with the DC-DC adapter. I took the time to add 45A Anderson PowerPole connectors and use 12GA wire to connect everything. I left the current set to 4A, but I dialed the voltage up to 48v. Why go up to 48v? I have not ever seen a 44.5v DC adapter, but I've seen several sources of 48v DC adapters at 3A/144W for under $20. If one of these will work with an OP403 then folks can potentially double their OP403's charge rate with a $20 Adapter and all they'd need to do is cut and splice two wires.

4.0Ah OP40401 Battery on Ryobi OP403 Charger with 48v@4.0A DC-DC Adapter

Charger OP403 (8v@4.0A DC-DC Adapter)
Battery OP40401 (rated 4Ah / 144Wh)
Total Charge Time 0:54:51 (3,291 sec)
Current In 3.6298A
"Bulk" charge rate 4.00A
Average charge rate4.008A
Measured Capacity 3.525Ah / 127.71Wh (88.1%)

Looks like a winner to me! This time the charge rate remained 4A for the entire charge cycle, no drop towards the end. The total charge time was within seconds of the previous time.

Several weeks have elapsed since my last test and in that time I've picked up an AC Adapter rated 48v at 3A (144W). I'm actually a bit excited to give this a try! I wired it up and plugged it in, but it did not charge the battery. I checked the wires then put a meter on the output to discover that the output voltage was bouncing around between about 24v and 32v. The charger was attempting to draw more current than the 48v AC Adapter could draw, and rather than deliver it's maximum 3A at a lower voltage (e.g., constant current mode) it simply bugged out. This option is completely a bust, though I suppose I could try to put a current limiting circuit on there.

Again after several more weeks I've picked up a Mean Well model ELG-240-48A-3Y LED Power Supply. eBay sure can be a good source for discounted equipment, can't it? This unit features adjustable output voltage (44.8v-51.2v), adjustable output current (2.5A-5.0A), and on overload it switches to a constant current mode (lowers voltage as needed to maintain rated current). It's exactly what I'm looking for! I wired it up and adjusted the output to 45v. I briefly connected the unit to a OP403 charger with a completely depleted 40v battery, then adjusted the output current until the battery measured a 4.0A charge current. Then I disconnect the battery and fully discharged it, then began a full charge cycle.

4.0Ah OP40401 Battery on Ryobi OP403 Charger with Mean Well ELG-240-48A-3Y set at 45v@4.0A

Charger OP403 (45v@4.0A)
Battery OP40401 (rated 4Ah / 144Wh)
Total Charge Time 00:53:56 (3,236 sec)
Current In 3.5669A
"Bulk" charge rate 4.01A
Average charge rate4.011A
Measured Capacity 3.273Ah / 117.64 Wh (81.8 %)

Perfect! The 4.0A charge current was maintained for the entire charge cycle, and the charge cycle lasted just 54 minutes. It's really amazing how steadily the Mean Well ELG-240-48A-3Y maintained the output current. To give some idea of how steady: 99.78% of all data points collected measured 4.01A +- 0.01A, and a further 0.18% were at 3.99A.

If anyone wants to upgrade the charge current from their OP403, the Mean Well ELG-240-48A is a perfect match. Don't forget to adjust the output voltage down to 45v and the current to match the Ah rating of your battery pack!

Final Thoughts on modding your OP403

It's worth noting that dumping a 1C charge rate into lithium-ion cells until they reach their maximum voltage of 4.2v is NOT the best way to charge them. The BEST way to charge lithium-ion cells is debatable (and depends on one's goals), but likely would involve the use of a multi-stage charger which includes both constant current (CC) and constant voltage (CV) stages. One must consider the desired charge time, final cell state of charge, and cell longevity. See the Battery University course "BU-409: Charging Lithium-ion" for details. In short, cell manufacturers rate how many cycles a cell can be recharged, providing that the maximum cell voltage and charge current are not exceeded. I believe this also assumes the use of a typical CC-CV charger. According to the BU-409 course, a lithium-ion cell charged via CC to 4.2v achieves approximately 85% of its capacity. If you'll compare the charge levels from everything done in this section, you'll see that the battery's state of charge doesn't reach the same level it did when charged with the OP400 and OP401 chargers. Fast charging via CC mode only at the 1C rate can get you back to work in under an hour, but this technique will likely rob you of about 15% of your battery's potential energy. So fast charge your battery only when you're in a hurry and use a CC-CV charger when you're not.

As mentioned previously, the OP403/OP404 are CC-only chargers. According to Battery University BU-409, cells charged with CC-only mode achieve approximately 85% of their capacity. I suspect that this 85% figure depends on the charge rate -- that charging at a faster rate will achieve a lower state of charge (SOC) while a slower rate will achieve a higher SOC. But I have no data available to suggest at what charge rates the change SOC becomes small. What do I mean? Let's say that fully charging via CC at the 1C rate results in an 85% SOC for our battery. If we charge at the 0.1C rate (10x slower) I'd expect our battery to achieve a much higher SOC, maybe 95%. If we charge at a rate in the middle of these two (0.55C) should we expect the SOC to be in the middle at 90%, or will it be skewed? It could be that the effect is negligible once the CC rate drops below some charge rate threshold. I suspect that this is the case, else why would Ryobi bundle the CC-only OP403/OP404 chargers as their go-to chargers for the 40v line?

Summary and Conclusions

Ryobi's fastest 40v charger is the OP406A, and it is MUCH faster than all other models. Don't use the OP406A as your standard charger for batteries under 6.0Ah in capacity.

Update 18-Feb-2021: The newly released OP407 3-port Quick Charger is now the second fastest in Ryobi's lineup of 40v chargers. It does charge batteries under 4Ah faster than I'd recommend, but it actually decreases its charge rate for these lower capacity batteries, which is good. This charger keeps up to three batteries ready for you next job. While working, it can be quickly charging two batteries while you are using the third. This won't be fast enough to keep you going continuously if you're using three batteries and a leaf blower, but it could be fast enough to keep up with most other tools.

The next fastest Ryobi 40v charger is the OP400, then comes the OP403 and OP404, and in last place comes the OP401. The difference in charge rate / charge times for these four models is not large. Basically the slowest OP401 charges at 1.25A, the OP403/OP404 is 20% faster at 1.5A, and the OP400 is 40% faster than the OP401 at 1.75A. The 4Ah battery I used for testing clocked a time of 2:23 on the fastest OP400, 2:35 on the OP403, and 3:13 on the slowest OP401. You can save some time by choosing the OP403 over the OP401, but the charge time is so long that no matter which of these you choose if you have just one battery you'll likely need to interrupt what you're doing and wait for the charger to do it's job.

The OP403/OP404 chargers could easily become the second fastest chargers by simply replacing the 42v 1.5A OEM power supply. If you plan to do this, be certain to select an AC adapter which reverts to constant current mode when overloaded. With a Mean Well ELG-240-48A adjusted to 45v output, one could adjust the output current from 2.5A to 5.0A. Testing above with the charge current set at 4A showed a charge time of 54 minutes, only about 1/3 of the 2.5 hours recorded when using the unmodified OP403. Just don't set the current output larger than the Ah rating of your battery. I'm certain that the increased charge current will be safe for your Ryobi 40v battery. I've now performed several charge cycles with several adapters rated up to 4A, and these did not overload the OP403's circuitry. But I cannot be certain that this stress will not eventually damage the charger or start a fire, so if you try this please be careful!

Before purchasing the OP407 3-Port Quick Charger, my strategy was to only use the OP406A rapid charger while actually working. One depleted battery on the OP406A will likely be fully recharged before I need it again. The slower chargers will be used when I'm not in a hurry to get back to work. I'll probably use a "turbo charged" OP403 instead of the OP406A for batteries rated under 6.0Ah. When I'm done for the day, I won't be using the OP406A or the "turbo charged" OP403. I'll use the standard slow chargers instead.

But now that I own an OP407 3-Port Quick Charger, my strategy will be to use the OP407 for all of my batteries rated 4Ah and up. I'll use the slower OP400/OP401 chargers with my batteries rated under 4Ah. I'll use the OP406A only with 6Ah and larger batteries and I hope to use it with higher capacity batteries when they're available. (Ryobi's manual for the 7.5Ah battery suggests that 9Ah and 12Ah batteries will be released at some time, and as of Mar-2022 the ryobitools website indicates 8.0Ah and 12Ah batteries "coming soon".)

One more thing: I don't leave my fully charged 40v batteries plugged into the chargers all the time. I have a number of OP400 and OP401 chargers, all wall mounted in my garage or shop. Once a battery has reached a full charge, I "un-click" it from the charger but leave it hanging there so I'll know where it is for next time. I haven't quite figured out what to do with the OP406A yet, maybe one day I'll replace one of the existing OP400/OP401 chargers. I have several OP403 chargers, which I keep in the camper, in the truck, in the shop, etc.

I find it very strange that all of the Ryobi 40v chargers have a slower "bulk" charge rate than the Ryobi 18v chargers (aside from the OP406A and OP407). I wonder why that is? The Ryobi 40v chargers have a "bulk" charge rate of 1.25A to 1.75A. The Ryobi 18v chargers have a "bulk" charge rate of 1.8A to 2.9A (aside from the overnight/trickle chargers). Therefore the fastest "normal" 40v charger is slower that the slowest "normal" 18v charger. What's up with that, Ryobi?!

Note: Additional testing results can be found here: Ryobi 40v Charger Testing #2

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Last revised 09-May-2022
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