Can I mix AH cells to make a larger battery?

[MT59918]

I’ve been using my 2 DIY 24v batts now for 2 years. One pack is 270ah or 280 I don’t remember. I’ll have to find the paperwork. The other pack is 310ah. I bought the cells from alibaba in the end of 2020 and they were delivered in 2021. Back then I got what I could get at the time. After 2 years I’m thinking about upgrading to a 48v system. I wan to go with server rack batteries but at the same time I’m wondering if I can utilize these cells as well for now. I’d like to maybe just buy one server rack battery a year to spread that cost over time.

Anyway my question is after searching and reading a few other post it seems okay to mix the 2 size cells 280-310ah into one battery bank to build a new 48v battery and just get a new BMS? Is my thinking correct? It seems that the battery will just be a 280ah and the 310 cells will not be utilized to full capacity.

Is my thinking correct? Any recommendations for a 48v BMS that’s available today? I’m out of the loop since I built my system 2 years ago I really haven’t had to do anything with it and had no issues.

Thanks for the help.

 

[Supervstech]

It may work, but your BMS will frequently shut down when the smaller cells reach full, and it will cause the smaller cells to wear out MUCH faster, since they would be peak charged every charge cycle.
Odds are good the BMS won’t last long either since it would be constantly trying to balance the weak cells…

 

[TorC]

AIUI, if you maintain a top balance and stay out of the lower knee, you'll probably do OK using it as a 280Ah battery, but you will still wear the 280Ah cells faster. All the cells should generally hit upper knee at about the same time if properly top balanced. It's possible you'll run into more issues if the internal resistance differs between the cells, though.