Capacity (Ah)  Model(s)  Cell Configuration  Capacity per cell (Ah)  Cells(s) Used  Specs 
1.5  OP4015  10S1P  1.5Ah  LG HB2  1500mAh,30A,3.65v 
2.0  OP40201  10S1P  2.0Ah  LG HD2?  
2.6  OP4026, OP40261  10S2P  1.3Ah  LG HA1 Samsung INR1865013  1300mAh, 15A, 3.68v 1300mAh, ??A, ??v 
3.0  OP4030, OP40301  10S2P  1.5Ah  Samsung 15Q?  
4.0  OP4040, OP40401  10S2P  2.0Ah  LG HD2?  
5.0  OP4050, OP40501  10S2P  2.5Ah  LG HE2?  
6.0  OP40601  10S2P  3.0Ah  LG HG2?  
6.0  OP40602  10S3P  2.0Ah  LG HD2?  
7.5  OP40752  10S3P  2.5Ah  LG HE2?  
8.0  OP4080  ???  ???Ah  ???  
9.0  OP40902  ???  ???Ah  ???  
12.0  OP4012A1  ???  ???Ah  ??? 
4Ah OP40401 Battery on Ryobi OP401 Charger  


4Ah OP40401 Battery on Ryobi OP403 Charger  


4Ah OP40401 Battery on Ryobi OP406A Charger  


OP4015 contains 1.5Ah cells. 1C rate = 1.5Ah/1hr = 1.5A. 6.15A > 1.5A
OP4020 contains 2.0Ah cells. 6.15A > 2.0A
Cell capacity is half that of the battery pack, since the design is two cells in parallel.
Each string of ten cells receives half the charge current, or 6.15/2 = 3.08A.
OP4026 is rated 2.6A, so the cells are 1.3Ah. 3.08A > 1.3A
OP40261 is rated 2.6A, so the cells are 1.3Ah. 3.08A > 1.3A
OP4030 is rated 3.0A, so the cells are 1.5Ah. 3.08A > 1.5A
OP40401 is rated 4.0A, so the cells are 2.0Ah. 3.08A > 2.0A
OP40501 is rated 5.0A, so the cells are 2.5Ah. 3.08A > 2.5A
OP40601 is rated 6.0A, so the cells are 3.0Ah. 3.08A > 3.0A
Cell capacity is one third that of the battery pack, since the design is three cells in parallel.
Each string of ten cells receives one third the charge current, or 6.15/3 = 2.05A.
OP40602 is rated 6.0A, so the cells are 2.0Ah. 2.05A > 2.0A
OP40751 is rated 7.5A, so the cells are 2.5Ah. 2.05A < 2.5A
I recommend using the OP406A sparingly or not at all on batteries under 6.0Ah in capacity. 
4Ah OP40401 Battery on Ryobi OP407 Charger  


Battery Model(s)  Rated Capacity (Ah)  ACTUAL Capacity (Ah) / % of Actual 
Recharge Time on Charger Model  

OP400  OP401  OP403/OP404  OP406A  OP407  
OP40601  6.0  5.515 / 92%  3:36:34 (12,994 sec)  5:40:07 (20,407 sec)  3:52:01 (13,921 sec)  1:15:51 (4,551 sec)  1:39:37 (5,977 sec) 
OP40401  4.0  3.675 / 92%  2:23:23 (8,603 sec)  3:13:37 (11,617 sec)  2:35:29 (9,329 sec)  48:40 (2,920 sec)  1:07:21 (4,041 sec) 
OP4026  2.6  2.305 / 89%  1:27:32 (5,252 sec)  1:57:45 (7,065 sec)  1:33:29 (5,609 sec)  N/A  0:48:57 (2,937 sec) 
4Ah OP40401 Battery on Ryobi OP403 Charger with extra power supply  


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


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


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


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


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


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


4.0Ah OP40401 Battery on Ryobi OP403 Charger with Mean Well ELG24048A3Y set at 45v@4.0A  

