Valence U1-12XP 12.8v 40ah 512wh Lifepo4 Battery

We opened each battery and they are perfectly balanced. There are 6 security bolts on the lid that come out easy.

The batteries have a BMU which communicates to another system so you will have to add a BMS. This is a nice power module that can handle up to 80a continuous discharge. We have 4s 30a BMS units for cheap too. It is very easy to add a BMS to this since the balance leads are right there and the main B- and C- are bolted connections.

Another great option would be to buy 4 of these and one 16s BMS so you can make a 51.2v 40ah battery.

Specs are in the 2nd photo.

They were all recovered in working and slightly used condition from hospitals.