toolboy's Corner: Charging Your Phone with a Ryobi Battery

What's the most energy efficient way to charge your Phone with a Ryobi 18v or 40v battery?

Imagine a situation where you want to be able to charge your smart phone as many times as possible with the Ryobi batteries that you have on hand. Perhaps you are camping and you won't have access to household power for a week or more, or you've experienced a widespread natural disaster such as a hurricane and you know that power won't be restored for at least a week. If your family has four phones you may want to keep one or all charged for as many days as possible until power is restored at your house. Let's say you have one fully charge 4Ah 18v battery. Does it matter if you use the USB-A output of your 150W Inverter or of your P743 Power Source if you want to maximize the number of charges?

My expectation is that which solution you choose does matter and that some charging solutions will be more energy efficient than others. I'd like to confirm this and to determine if the difference is great enough to be concerned about. Some of my expectations are: Of the available off-the-shelf ("OTS") solutions, my expectation is that the most energy efficient solutions will be the P743 (USB-A) for 18v and the OP403 (USB-A) for 40v, because these solutions provide USB output only and don't waste energy keeping AC outputs energized. I'm also thinking that some "home brew" solutions may be more energy efficient than any of the OTS solutions because the OTS solutions either have the energy wasting AC inverter or do not implement QC/PD and are therefore limited to a maximum charge rate of about 10W (5v at 2A).

Some combinations that I'll test: I will also test some home brew solutions: Be aware that the results presented here are not necessarily representative of all devices involved. Different smart phones consume energy differently, and the difference could be significant. I'll also attempt to determine how efficient wireless charging is compared to wired. The efficiency of wireless chargers can vary greatly and may correlate to the rated charge rate: 5W, 7.5W, 10W, 15W. Also, an AC adapter and an In-Vehicle adapter are used for some of these tests and the differences in adapter efficiency could be significant.

Equipment used for testing

The smart phone I've selected for testing is an iPhone XR, which has an internal battery rated 2942mAh/11.16Wh. My particular iPhone reports a battery health maximum capacity of 86%. My guess is that this suggests the battery's actual capacity is (11.16Wh)(0.86)= 9.6Wh, but who knows for sure. Before each test I ran the iPhone until it was totally dead. I did NOT turn off the cell service or the Wi-Fi as I suspect that this is more representative of how most folks will charge their phones. But be aware that disabling these and all background tasks could improve the results, perhaps significantly. During the test I did not use the iPhone at all, in hopes of maximizing the charger's energy to recharging the battery rather than powering the screen or running apps (though I did occasionally touch the screen to see the charge level). This iPhone model claims to be capable of being charged with higher than 5v via USB-C PD and up to 15W wireless charging with MagSafe.

As per Apple, the maximum charge rate for the iPhone XR is 18W, via a USB-C cable. The maximum charge rate for various iPhones is:

In-Vehicle Charger

For the "home brew" testing I used a Sundaree In-Vehicle charger, which is rated for 12-24v input. This input range is wide enough that it can be powered directly by a Ryobi 18v battery. In order to use the Sundaree with a Ryobi 40v battery the battery is first connected through a 36v-to-12v buck converter. The Sundaree features dual USB-C PD 20W and dual USB-A QC 18W output ports. This means that the Sundaree is capable of charging an iPhone XR at its maximum rate with either USB-A or USB-C. However, this Sundaree does not provide enough power to charge an iPhone 11, 12, or 13 at their maximum rates.

Wall Charger

For some tests I plugged an AC wall charger into the AC output of a Ryobi inverter. The unit I'll be using is an MCY Model LX-PQ065AU 65 Watt 3 port foldable USB-C Charger GaN Tech Fast Charger. The MCY has two USB-C and one USB-A output. The specs claim support of full quick charge protocols including Apple PD 3.0, Android QC4+, QC 3.0, AFC, MTK, etc. The USB-C is rated up to 65W out, USB-A up to 30W out.

Wireless Charging Pads

I do not have a tool to measure the actual charge delivered wirelessly. But once the phone's battery reaches full charge we should be able to compare the results achieved using a wireless pad with the results achieved when wired directly to the same power source with the same type of cable.

An Onn 5W Wireless pad was used for testing first generation wireless charging technology. This wireless pad uses a 5v-only, USB-A cable.

A RAVPower model RP-WC012 was used to represent the latest wireless charging technology. The specs for this unit indicate input 5v/2A or 9v/2.22A and output 15W max. That's an input of 10W @ 5v or 19.98W @ 9v. so obviously 9v is required in order to have any chance of achieving the 15W output. This MagSafe wireless pad uses a USB-C/PD cable.

It took several failed attempts before I was actually able to capture my first full charge cycle of the iPhone XR with my datalogger. Apparently the memory card I was using to capture the raw data was faulty and I lost results twice before I realized that the problem was the SDHC memory card. In that time I observed that using USB-C the iPhone charged to 86% in one hour and to 96% after two hours. I wonder if charging to a full 100% is sensible, given that it took longer to achieve that last 14% that it took to achieve the first 86%. Perhaps it would make more sense to stop the test when a predetermined amount of energy has been delivered to the iPhone, say when the phone has reached 85% of a full charge. If the battery's capacity is 9.6Wh then 85% is (9.6Wh)(0.85) = 8.16Wh

I've reported elsewhere on this site that the ACTUAL capacity of the Ryobi 18v and 40v batteries is less than the rated capacity. For a new battery we should assume that the ACTUAL capacity is 95% of rated capacity, for used batteries assume 90% (or less). The batteries I'll be using for testing are used, so let's assume that the ACTUAL capacity of my 18v 4Ah battery is (18v)(4Ah)(0.90)= 65Wh and that the ACTUAL capacity of the 40v 4Ah battery is (36v)(4Ah)(0.90) = 130Wh. (Note that a Ryobi 40v battery is more accurately a 36v battery, calling it 40v is a marketing thing. Also, during the time it took to perform all of this testing I purchased a couple of PBP007 Ryobi 18v HIGH PERFORMANCE 6Ah batteries, each of which tested at 98% of rated capacity.)

Therefore I expect that the theoretical maximum number of full recharges of my iPhone XR and no energy losses (hah!) will be (130Wh)/(9.6Wh)= 13.5 with my used 40v 4Ah battery and (65Wh)/(9.6Wh)= 6.8 with my used 18v 4Ah battery.

Ryobi claims regarding the anticipated number of phone charges

The Ryobi Inverters make various claims wrt. the number of charges which will be possible with specific batteries, see the images below. For example, the 40v 300W Inverter advertising includes a table which indicates that a 40v Ryobi 4Ah battery can charge the average phone 15.1 times, and the 18v 150W Inverter advertising indicates that an 18v Ryobi 18v battery can charge the average phone 6.3 times. These numbers are not so far from the calculations in the previous paragraph which suggests 13.5 charges with my used 40v battery and 6.8 charges with my used 18v battery. Let's test these and find out!



P743 18v ONE+ Portable Power Source (USB-A/2.1A)

This device has exactly one purpose, which is to provide USB power from a Ryobi 18v battery. The P743 has two USB-A ports, one rated 2.1A max and the other rated 1.0A max. For this test, I used the 2.1A port.

iPhone XR using 18v battery and P743 (USB-A/2.1A)

Device P743
(USB-A, 5v/2.1A max)
Battery P194 18v (rated 9Ah / 162Wh)
Total Charge Time 2:45:45 (9,945 sec)
Watts Out/Battery 16.45Wh
Watts Out/Charger 12.99Wh
Idle Draw (est.) 0.4W
Efficiency 79%

The CC rate starts at about 13W and tapers to 11W at 0:59, at which time the CV rate begins. The charge appears to level off around 2:30. However, the USB dongle which was used to measure the USB output cut off at 2:45:45. It took 16.45Wh to fully charge the iPhone XR with this configuration, so we'll be able to charge our phone about (68.4Wh)(16.45) = 4.2 times with a new 4Ah 18v battery.

P743 18v ONE+ Portable Power Source (USB-A/1A)

The P743 has two USB-A ports, one rated 2.1A max and the other rated 1.0A max. For this test, I used the 1.0A port.

iPhone XR using 18v battery and P743 (USB-A/1A)

Device P743
(USB-A, 5v/1A max)
Battery P194 18v (rated 9Ah / 162Wh)
Total Charge Time 3:06:00 (11,160 sec)
Watts Out/Battery 16.06Wh
Watts Out/Charger 12.55Wh
Idle Draw (est.) 0.4W
Efficiency 78%

The CC rate starts at about 8W and remains steady throughout the CC charge. The charge changes to CV around 1:34. The charge appears to level off around 3:01. However, the USB dongle which was used to measure the USB output cut off at 3:06:00. It took 16.06Wh to fully charge the iPhone XR with this configuration, so we'll be able to charge our phone about (68.4Wh)(16.06) = 4.3 times with a new 4Ah 18v battery. Conclusion: the iPhone XR charges slightly slower with the 1A port as compared to the 2.1A port, but the energy efficiency is the same.

RYi150BG 18v ONE+ 150 Watt Power Source (USB-A)

The RYi150BG has an AC output of 120v at up to 150W with a modified sine signal, and USB-A with a maximum draw of 2.4A.

iPhone XR using 18v battery and RYi150BG (USB-A)

Device RYi150BG
(USB-A, 5v/2.4A max)
Battery P194 18v (rated 9Ah / 162Wh)
Total Charge Time 2:02:17 (7,337 sec)
Watts Out/Battery 20.74Wh
Watts Out/Charger 13.25Wh
Idle Draw (est.) 3.6W
Efficiency 64%

The CC rate starts at about 15W and slowly decreases to 12W at 1:06, at which time the CV rate begins. The charge appears to level off around 2:02. I snapped a photo at 1:21:53 which shows 11.50Wh delivered at a cost of 17.80Wh from the 18v battery, so I'm thinking that it might be a good idea to stop the charge cycle around 90 minutes. If you don't power down the Inverter, it will continue to consume about 3.6 Watts of energy until you do or the battery is fully depleted. It took 20.74Wh to fully charge the iPhone XR with this configuration, so we'll be able to charge our phone about (68.4Wh)(20.74) = 3.3 times with a new 4Ah 18v battery.

Home Brew USB-C Solution with 18v Battery

I wired an in-vehicle USB charger directly to my 18v battery to conduct this test. The in-vehicle USB charger was rated for an input of 12v to 24v so a step-down voltage converter was not required in order to power it from an 18v battery (whose output can range from 21v when fully charged down to about 14v when fully discharged and just before the battery protection circuit engages).

iPhone XR using 18v battery and Sundaree 4-Port Charger (USB-C)

Device Sundaree 4-Port In-Vehicle Charger
(USB-C PD 20W max)
Battery P194 18v (rated 9Ah / 162Wh)
Total Charge Time 1:33:30 (5,610 sec)
Watts Out/Battery 13.69Wh
Watts Out/Charger 12.06Wh
Idle Draw (est.) 1.63W
Efficiency 88%

I observed that the charge started with a 5v output, but after about one minute the iPhone "booted" and the USB-C output changed to 9v. For the first minute (before the iPhone "booted") the output was about 14W. Then the charge rate jumped to 20W, tapered to 14W at 15 minutes, held at 14W until 30 minutes, tapered to 10W at 40 minutes, then held at 10W until the CV started at 51 minutes. The last data point where more than 2.00 Watts was drawn from the 18v battery occurs at 1:33:30, which I'll call "end of charge". At this point I measured 13.69Wh drawn from the 18v battery and 12.06Wh delivered via USB-C, and the iPhone reported 96% charged. It took 13.69Wh to fully charge the iPhone XR with this configuration, so we'll be able to charge our phone about (68.4Wh)(13.69) = 5.0 times with a new 4Ah 18v battery.

P743 18v ONE+ Portable Power Source (USB-A and 5W Wireless Pad)

Earlier we determined that the two USB-A outputs on the P743 had nearly the same efficiency when charging the iPhone XR, so now let's see if switching from wired charging to makes a difference. The Onn 5W Wireless pad is a first generation device for wireless charging.

iPhone XR using 18v battery, P743 to 5W Wireless Pad

Device P743
(USB-A, 5v/2.1A max)
Onn model ONB18W1701 5W pad
Battery P194 18v (rated 9Ah / 162Wh)
Total Charge Time 7:53:10 (28,390 sec)
Watts Out/Battery 24.55Wh*
Watts Out/Charger 17.91Wh*
Idle Draw (est.) 3.0W/0.2W*
Efficiency 73%*

So apparently the charge never actually completed. The test ran for 15 hours before I returned to check, at which time the P743 had shut itself off and the iPhone XR reported that it was charged to 92%. The data shows that the battery had been delivering 3.0W for nearly eight hours before dropping suddenly to 0.2W, which must have been when the P743 powered down. The charge rate was so slow that there is no visible change from CC to CV mode in the curve.

* In the cases where a Lightning cable was used, the iPhone reached 100% charge with 12Wh-13Wh out from the USB port. But with the 5W wireless pad the P743 powered down before the iPhone reached a full charge. The iPhone indicated 92% charged and the data indicate 24.55Wh Watts Out from the battery and 17.91Wh dispensed to the wireless 5W pad. So with the 5W pad 24.55Wh was required from the battery to achieve a 92% charge. If the test had continued until the iPhone reached 100% charge this number would have been even higher, which makes this scenario the least energy efficient solution (so far). This configuration drew 3W until the unit shut down at 8 hours, and it drew 0.2W thereafter.

Home Brew USB-C Solution with 18v Battery and 15W Wireless Pad)

The 5W wireless pad was less efficient that the wired solution, but is this also true for a 15W wireless pad? I used a RAVPower 15W wireless charging pad for this test, model RP-WC012. The specs for this unit indicate input 5v/2A or 9v/2.22A and output 15W max. That's an input of 10W @ 5v or 19.98W @ 9v. so obviously 9v is required in order to have any chance of achieving the 15W output. However this may not matter as the iPhone XR's max wireless charging rate is 10W. I removed the protective case from the iPhone XR to ensure optimal charging.

iPhone XR using 18v battery, Sundaree 4-Port Charger (USB-C), RAVPower 15W Wireless Pad

Device Sundaree 4-Port In-Vehicle Charger
(USB-C PD 20W max)
RAVPower 15W Wireless MagSafe pad
Battery P194 18v (rated 9Ah / 162Wh)
Total Charge Time 3:27:07 ( sec)
Watts Out/Battery 21.27Wh
Watts Out/Charger 18.02Wh
Idle Draw (est.) 2.0W
Efficiency 56% - 61%*

The charge curve shows a CC/CV curve. The charger drew about 5W for the first 5 minutes, then jumped to 11W for 15 minutes, then dropped to 7W until 1:45, then held about 6.5W until 2:23 when the CV began.

* In the cases where a Lightning cable was used, the iPhone reached 100% charge with 12Wh-13Wh out from the USB port. But with the 15W wireless pad, 18W was required from the USB-C port to achieve a full charge. A calculation of efficiency is somewhat of a guess as the actual quantity of charge delivered to the iPhone's battery was not measured. If we guess it was 12Wh, then the efficiency was (12Wh)/(21.27Wh) = 56%. If we guess 13Wh, the efficiency is (13Wh)/(21.27Wh) = 61%

RYi120A ONE+ 18V 120-Watt 12V Automotive Power Inverter with Dual USB Ports (USB-A)

I picked up one of these inverters for under $20 and decided that I should go ahead and perform a phone charge test with it. With this inverter Ryobi provides an 18v battery connector which does not "click" to lock on the battery, and I've found that this means the setup is somewhat prone to coming disconnected if it gets jostled during use.

iPhone XR using 18v battery, RYi120A ONE+ 18V 120-Watt 12V Automotive Power Inverter (USB-A)

Device RYi120A ONE+ 18V 120-Watt 12V Automotive Power Inverter
(USB-A 2.4A max)
Battery P108 18v (rated 4Ah / 72Wh)
Total Charge Time 2:36:21 ( sec)
Watts Out/Battery 20.24
Watts Out/Charger 16.06Wh
Idle Draw (est.) W
Efficiency %

This does look pretty much like a CC/CV curve, though interestingly it can be seen that during the CC phase there's a small spike every five minutes (See 2:40, 7:42. 12:44, 17:46, etc.) After each of these small spikes, the current draw is adjusted slightly. These spikes do not appear in the CV portion of the curve. I was not present when the iPhone reached a full charge, but my USB-A meter terminated with 16.06Wh drawn. After examining the data I estimate the end of charge occurred at 2:36:21. It took 20.24Wh to fully charge the iPhone XR with this configuration, so we'll be able to charge our phone about (68.4Wh)(20.24) = 3.4 times with a new 4Ah 18v battery.

* In the cases where a Lightning cable was used, the iPhone reached 100% charge with 12Wh-13Wh out from the USB port. But with the 15W wireless pad, 18W was required from the USB-C port to achieve a full charge. A calculation of efficiency is somewhat of a guess as the actual quantity of charge delivered to the iPhone's battery was not measured. If we guess it was 12Wh, then the efficiency was (12Wh)/(21.27Wh) = 56%. If we guess 13Wh, the efficiency is (13Wh)/(21.27Wh) = 61%

OP403 40v Charger (USB-A)

The OP403 charger will charge your 40v battery, but it also has a USB-A port which can be used to power devices such as a cell phone charger. The USB port can be used while the charger is connected either to AC power or to a 40v battery and it is fairly small.

iPhone XR using 40v battery and OP403 (USB-A)

Device OP403 Charger with USB-A
(USB-A, 5v/2.1A max)
Battery OP40601 (rated 6Ah / 216Wh)
Total Charge Time 2:42:18 (9,738 sec)
Watts Out/Battery 26.49Wh
Watts Out/Charger 12.14Wh
Idle Draw (est.) 3.3W
Efficiency 46%

The curve looks very confusing. Evidently the OP403 spikes and draws about 4A for one second every 55 seconds. That's a spike of 160W-170W when just before and just after these spikes the draw is in the range of 2W to 12W! Ignoring these remarkably large spikes, the plot shows the overall process resembles a CC/CV curve. The CC rate starts at about 12W and rapidly declines to 10W after about 6 minutes. The CC rate then slowly declines to 7W 1:54, at which time the CV rate begins. Looking at the curve it's clear that the charge never completely ends, but it appears to level off at 2W around 2:42. The iPhone XR indicated a charge level of 98% at 2:42. It took 26.49Wh to fully charge the iPhone XR with this configuration, so we'll be able to charge our phone about (136.8Wh)(26.49Wh) = 5.2 times with a new 4Ah 40v battery.

Note: due to the big spikes every 55 seconds the average idle draw of the OP403 is about 3.3W. So your OP403 will draw 3.3W every hour that you leave your battery connected even after your phone has reached 100% charge.

RYi300BG 40v 300W Inverter (USB-C)

The RYi300BG has an AC output of 120v at up to 300W with a pure sine signal, USB-A and USB-C ports. For this test we'll use the USB-C port.

I performed this test more than once, not because I wanted to but because I discovered during testing that my 300W inverter was faulty at the time I tested other devices and several months elapsed before I purchased a new 300W Inverter. With my new 300W Inverter, I first set up the test to charge my iPhone XR near the end of the day, and I didn't return until the next morning. BIG MISTAKE. Sure, the 300W Inverter charged the iPhone XR just fine, probably in under 2 hours. But after the iPhone reached a full charge, the 40v battery continued to keep the 300W inverter energized all night until I turned it off the next morning. My 6Ah battery had started with a full charge, but it had run down to one bar by keeping the inverter on overnight. The 300W inverter draws about 8.5 Watts per hour when energized. So this experiment drained my 6Ah battery an estimated (16 hours)(8.5W) = 136Wh plus another 15Wh or so to actually charge the phone. That's over 150Wh drawn from my 40v battery to put an estimated 12Wh charge on my iPhone XR. Not so good. At this rate I won't be able to fully charge my iPhone XR twice before my 6Ah battery is depleted. If you plan on using your 300W inverter just for charging your phone:

Be certain to power down your inverter ASAP after your phone has reached a full charge!



On my next attempt, I babysat the test setup. At 90 minutes I checked the iPhone XR charge level, which was 95%. I didn't really want to check the iPhone often, as doing so drains the battery a bit to power on the display, and this can skew the results. I didn't check again until 152 minutes, at which time the iPhone charge level was at 100% so I stopped the test. Following a careful review of the data I'm going to declare that the iPhone XR reached a full charge at 1:49:36 as this is when the power draw reached a minimum.

iPhone XR using 40v battery and RYi300BG 300W Inverter (USB-C)

Device RYi300BG 300W Inverter (USB-C)
(USB-C, 5v/2.1A max)
Battery OP40601 (rated 6Ah / 216Wh)
Total Charge Time 1:49:36 (6,576 sec)
Watts Out/Battery 27.48Wh
Watts Out/Charger 13.06Wh
Idle Draw (est.) 8.5W
Efficiency 47%


Once again, I must point out that the 300W Inverter continued to draw power from the battery once the phone had reached a full charge. I stopped the test at 152 minutes, but the iPhone XR reached a full charge after just 110 minutes. The battery continued to power the 300W Inverter for another 42 minutes, drawing at a rate of about 8.5W for that whole time. That's an additional (42 minutes)(1 hour/60 minutes)(8.5W) = 6Wh of energy which was totally wasted. It took 27.48Wh to fully charge the iPhone XR with this configuration, so we'll be able to charge our phone about (136.8Wh)(27.48Wh) = 5.0 times with a new 4Ah 40v battery.

RYi300BG 40v 300W Inverter (USB-A)

The RYi300BG has an AC output of 120v at up to 300W with a pure sine signal, USB-A and USB-C ports. For this test we'll use the USB-A port. At 90 minutes I checked the iPhone XR charge level, which was 95%. I didn't really want to check the iPhone often, as doing so drains the battery a bit to power on the display, and this can skew the results. I didn't check again until 152 minutes, at which time the iPhone charge level was at 100% so I stopped the test. Following a careful review of the data I'm going to declare that the iPhone XR reached a full charge at 1:49:36 as this is when the power draw reached a minimum.

iPhone XR using 40v battery and RYi300BG 300W Inverter (USB-C)

Device RYi300BG 300W Inverter (USB-A)
(USB-A, 5v/2.1A max)
Battery OP40601 (rated 6Ah / 216Wh)
Total Charge Time 2:11:15 (7,875 sec)
Watts Out/Battery 30.65Wh
Watts Out/Charger 12.89Wh
Idle Draw (est.) 8.5W
Efficiency 42%


I checked the progress at 1:18 and again at 2:02 the iPhone indicated 98% charge, then at 2:18 the iPhone indicated 100% charge. Upon review of the data between 2:02 and 2:18 minutes, frankly I cannot confidently find a point where I'd say the charge had come to an end. My best guess would be at 2:11:15, but the real end time could have been anywhere in that range. It took 30.65Wh to fully charge the iPhone XR with this configuration, so we'll be able to charge our phone about (136.8Wh)(30.65Wh) = 4.5 times with a new 4Ah 40v battery.

RYi300BG 40v 300W Inverter (AC to USB-C Adapter)

Is it more energy efficient to use an AC to USB-C adapter instead of the built-in USB-C port? I wouldn't think so, but let's test it to be certain.

iPhone XR using 40v battery with RYi300BG and MCY 120v AC Charger (USB-C/PD 65W)

Device RYi300BG 300W Inverter
MCY GaN model LX-PQ066AU
(USB-C/PD 65W max, USB-A/QC 30W max)
Battery OP40601 (rated 6Ah / 216Wh)
Total Charge Time 1:48:50 (6,530 sec)
Watts Out/Battery 30.02Wh
Watts Out/Charger 12.60 Wh
Idle Draw (est.) 9.0W
Efficiency 42%

The curve is nearly identical to the previous one where the Inverter's USB-C output was used directly, except that it's been shifted a little higher. So no, it's not more efficient to use an AC adapter with USB-C, just use the Inverter's built-in port. It took 30.02Wh to fully charge the iPhone XR with this configuration, so we'll be able to charge our phone about (136.8Wh)(30.02Wh) = 4.6 times with a new 4Ah 40v battery.

Home Brew USB-C Solution with 40v Battery

I am unable to wire my in-vehicle charger directly to a Ryobi 40v battery because the voltage out of the 40v battery is too high. So I used a 36v-to-12v step-down bucking converter to drop the voltage out of the 40v battery to 12v, then connected the in-vehicle charger to the 12v output of the converter. We will lose some energy due to the converter, but this device claims to be >90% efficient and this may be sufficient for a good overall result.

iPhone XR using 40v battery with 36v-to-12v converter and Sundaree 4-Port In-Vehicle Charger (USB-C)

Device 36v to 12v Converter (20A)
Sundaree 4-Port In-Vehicle Charger
(USB-C/PD 20W max)
Battery OP40601 (rated 6Ah / 216Wh)
Total Charge Time 1:39:11 (5,771 sec)
Watts Out/Battery 14.96Wh
Watts Out/Charger 12.13Wh
Idle Draw (est.) 2.63W
Efficiency 81%

I observed that the charge started with a 5v output, but after about one minute the iPhone "booted" and the USB-C output changed to 9v. For the first minute (before the iPhone "booted") the output was about 15W. The charge rate then jumped to 21W, tapered 15W at 15 minutes, held at 15W until 30 minutes, then tapered to 11W at 40 minutes, and held at 11W until the CV started at 51 minutes. This is exactly the same as what was observed when the Sundaree was powered directly by an Ryobi 18v battery, except for that one additional Watt of energy. And this isn't surprising, given that the charger is exactly the same. The only difference is the 36v-to-12v converter, and from the data it appears that this converter incurs a 1W overhead for the entire charge cycle.

Summary of Results

Results are collated below, grouped by battery voltage and sorted by the amount of energy required. The "# Charges" estimates the # charges to expect with a new 4Ah Ryobi battery.

Option Battery
(v)		 Energy Consumed
(Wh)		 Energy Delivered
(Wh)		 Efficiency
(%)		 Time
(HH:MM)		 # Charges
w/4Ah battery1		 Idle Draw (est)
(No Load)2
(W)
18v Battery
Sundaree 4-Port Charger
(USB-C/PD 20W max)		 18 13.69 12.06 88 1:33 5.0
P743 (USB-A/2.1A max) 18 16.45 12.99 79 2:46 4.2 0.41
P743 (USB-A/1A max) 18 16.06 12.45 78 3:06 4.3 0.41
P743
(USB-A/2.4A max)
5W Wireless pad		 18 24.55 17.91 73 7:533 2.8 0.41
RYi150BG 150W Inverter
(USB-A/2.4A max)		 18 20.74 13.25 64 2:024 3.3 2.62
Sundaree 4-Port Charger
(USB-C/PD 20W max)
15W Wireless pad		 18 21.27 18.02 56-61 3:27 3.2
40v Battery
36v-to-12v converter,
Sundaree 4-port Charger
USB-C/PD 20W max)		 40 14.96 12.13 81 1:39 9.2
RYi300BG 300W Inverter
USB-C port		 40 27.48 13.06 47 1:494 5.0 7.29
OP403 Charger/USB
(USB-A/2.1A max)		 40 26.49 12.14 46 2:42 5.2
RYi300BG 300W Inverter
+ USB-C Wall Charger
(USB-C 65W)		 40 30.03 12.60 42 1:484 4.6 7.29
RYi300BG 300W Inverter
USB-A port		 40 30.65 12.89 42 2:114 4.5 7.29
RYi300BG 300W Inverter
+ USB-C Wall Charger
(USB-A 20W)		 40           7.29


1 This is the estimated number of charges assuming that the charging operation is stopped immediately when the phone reaches 100% charge.
2 The estimated Idle Draw was determined by completely discharging a fully chaged 4Ah battery with no load.
3 The test results for the 5W wireless pad are based on an iPhone XR charge to 92%, not to 100%.
4 This test did not stop when the phone reached a full charge. The battery would likely have drained completely if left undisturbed.

Conclusions

Let's review my initial expectations and see My expectation is that some charging techniques will be more energy efficient than others. I'd like to confirm this and to determine if the difference is great enough to be concerned about. Some of my expectations are: The above tells us that the solutions which require the least energy from a Ryobi battery are the home brew solutions! With a new Ryobi 18v 4Ah battery we can expect (18v)(4Ah)(0.95 new)/(13.69Wh) = 4.99 full charges for my iPhone XR. With a new Ryobi 40v 4Ah battery we can expect (36v)(4Ah)(0.95 new)/(14.96Wh) = 9.15 full charges for my iPhone XR.

The most energy efficient Off-The-Shelf solution for 18v batteries is the P743 at 78% energy efficient, which is only a little bit less efficient than the 88% energy efficient "home brew" solution. Furthermore, the P743 features an extremely low idle draw (0.41W) and an automatic shutoff after 8 hours. So, unlike the Inverters, you can use the P743 to charge your phone overnight with no need to worry about draining your Ryobi battery significantly once your phone has reached a full charge.

Frankly, Ryobi's available solutions for charging a phone from their 40v platform are embarrassing. None of the 40v options reach 50% efficiency, which means that more than half of your 40v battery's energy is wasted when used for this purpose. The only unit which will terminate the charge immediately when your phone reaches a full charge is the OP403.

An important takeaway is that the Ryobi Inverters do not power down once the phone has reached a full charge, which makes them a terrible choice for charging your phone overnight or when unmonitored. What this means is that your battery continues to drain even though your phone has reached a full charge. If you leave your phone for 8 hours of overnight charging, the amount of energy drained can be 3X the amount needed to recharge your phone, or more.

How do the actual number of charges per 4Ah battery compare with my expectations and with Ryobi's claims?

For a used 18v 4Ah battery I had estimated that up to 6.8 charges should be possible with lossless charging. For a new 18v 4Ah battery and the 150W Inverter, Ryobi advertises 6.3 charges for a phone with "average capacity". The actual number of charges was tested and estimated to be 3.3, and this assumes that the Inverter is disconnected immediately after the phone reaches 100% charge. I'd say Ryobi's estimate is rather optimistic. With the most efficient configuration tested (the home brew solution!) we calculated the number of charges to be 5.0. Given that we calculated the most efficient solution as having 88% efficiency, my initial estimate of 6.8 lossless charges would be reduced to (6.8)(.88) = 6.0 lossy charges. I wasn't right on the money, but I'm satisfied with having guessed 6 and the tested answer is 5.

For a used 40v 4Ah battery I had estimated that up to 13.5 charges should be possible with lossless charging. For a new 40v 4Ah battery and the 300W Inverter, Ryobi advertises 15.1 charges for a phone with "average capacity". The actual number of charges was tested and estimated to be 4.6, and this assumes that the Inverter is disconnected immediately after the phone reaches 100% charge. I'd say Ryobi's estimate is extremely optimistic. With the most efficient configuration tested (the home brew solution!) we calculated the number of charges to be 9.2. Given that we calculated the most efficient solution as having 81% efficiency, my initial estimate of 13.5 lossless charges would be reduced to (13.5)(.81) = 10.9 lossy charges. Again, I wasn't right on the money but I'm satisfied with having guessed 11 and the tested answer is 9.

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Last revised 10-Oct-2022
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