This is a hypothetical question: I have a 40 kWh battery (96s2p). At some point in time, one of the cells may go bad. From what I can read from many sources is that it is a bad idea to replace an old module in an old pack with a completely new module. A module is 2s2p, i.e. I just need to change one series connected module
What I don't understand is why? Assuming the Leaf has a passive BMS, the "only" thing it does (in this respect, ignoring all other safety features!) it to bleed off residual charge when cell voltages gets too high.
Assuming all the old modules have a capacity of 50% of the new module and all modules (48 of them as far as I know) start off at the same voltage, then we just need to consider two scenarios:
I am pretty sure the Leaf does not have an active BMS, as in that case the arguments would be slightly different.
EDIT: Changed cell to module
What I don't understand is why? Assuming the Leaf has a passive BMS, the "only" thing it does (in this respect, ignoring all other safety features!) it to bleed off residual charge when cell voltages gets too high.
Assuming all the old modules have a capacity of 50% of the new module and all modules (48 of them as far as I know) start off at the same voltage, then we just need to consider two scenarios:
- Discharging: Here the old cells will discharge faster compared to the new cell as the capacity is smaller. But that only means that the new cell is not utilized fully.
- Charging: Here the old cells will charge faster compared to the new cell as the capacity is smaller. But again: That only means that the new cell is not utilized fully.
I am pretty sure the Leaf does not have an active BMS, as in that case the arguments would be slightly different.
EDIT: Changed cell to module
Last edited: