Building 48v pack from new and used?

[blerpaderpa]

I have 8 280Ah lifepo4 cells that were previously used in a 2x12v configuration. They’re about 5 years old and I only used them for about a year with very moderate use. How bad of an idea is it to put these into a 48v configuration with 8 brand new cells and just re-top balancing everything.

I was thinking of using the new overkill solar 48v bms when that shows up and plugging this into a Schneider XW Pro.

I just really don’t have a ton of use for these packs and would like to make use of them. Other creative usages welcome….

And if you guys poo poo this idea, what would be the best way to turn these into basic UPS backup batteries? They’re running 12v overkill bms’s right now

 

[BentleyJ]

Do you have a way of testing cell capacity to determine which cell has the lowest capacity. The 48V battery pack would then be limited to the Ah of that lowest cell.

For example say one used cell is 265Ah and the remainder of the old cells are all around 275Ah while the new cells are around 285Ah. The capacity value on the BMS or Shunt menu would be set to 265Ah. Which would translate to 265Ah x 51.2V = 13.6kWh of storage capacity. This is lower than the theoretical energy storage capacity of 14.3kWh.