I am aware it's best to use cells of the same capacity, same age, etc. However, until I can replace the cells I have I need to make use of these.
The batteries I have are 2V flooded lead-acid cells, 6x 400Ah and 12x 225Ah (both at C10). I need 12V at the highest possible capacity with the cells available (without destroying/overcharging any cells, obviously).
What I want to accomplish is parallel the 12x 225Ah to create a 12V 450Ah battery and then parallel this with the 6x 400Ah in series (=12V 400Ah) to yield 12V ~800Ah. This should not result in overcharging any cells, since only like voltages are paralleled.
It only should result in a slight underuse of the capacity of the 12x 225Ah cells (~11%), but that seems acceptable (especially since the 225Ah cells are a little older than the 400Ah cells, so their capacity is probably a little nearer to 200Ah anyway).
What would be the best way to connect the 12x 225Ah cells for this? I can think of two ways to connect the cells:
- Create six pairs of 2x 2V 225Ah in parallel and connect these 6 pairs in series, or,
- Create two strings of 6x 2V 225Ah in series, and parallel these two strings.
Am I correct in thinking that option 2 only yields 3x225Ah=675Ah in practice, since I am effectively paralleling 400Ah, 225Ah, 225Ah (and the 400Ah battery will perform as if it were a third 225Ah battery), while only option 1 will yield the desired 800Ah; paralleling 400Ah and (225Ah+225Ah=450Ah) (where the 450Ah battery will perform as a 400Ah)?
Also, am I perhaps missing another possible (better) way to connect these cells? Thanks!