openinverter forum

Hi everyone,
I’m currently experimenting with a DIY EV battery pack that, due to supply limitations, ended up with a mix of cells that have slightly different usable capacities (same chemistry, but not from the same batch).
I know that in an ideal setup, all cells should be matched as closely as possible, but in the real world, sometimes you have to work with what’s available. My concern is how best to handle balancing in this scenario.
- Would a traditional passive balancing BMS be enough, or would it constantly waste energy and heat trying to keep the cells aligned?
- Is an active balancing solution more practical here, or is it just overcomplicating things for small differences in capacity?
- At what point does the imbalance become serious enough that the pack's lifespan is significantly reduced?
Has anyone here tried running a pack with this kind of “imperfect” matching, and what were your long-term results?

Thanks in advance for any insights!

Imbalance just reduces usable capacity, not lifespan. So assuming all cells have even capacity but one cell sits at 70% while the others are full at 100% then only 70% of the whole pack can be used.

Using different capacity cells means the pack has the capacity of the weakest cell. Balancing will not cure that. Your best bet is top balancing at a high per cell threshold voltage. And tapering discharge current as the weakest cell runs dry

How many cells? These work great for smaller voltage battery packs, 16S 48v nom. You can overlap the last cell on the first balancer with the first on the second balancers and add another 15 cells and so on, but they aren't cheap to buy
https://zhcsolar.com/product/battery-balancer-192v/

T1 Terry