Good info Thanks for sharing

will APC ups with 2 batteries (24V) works fine with LiFePo4, does the voltage match without any circuit modification so they will get full charge and discharge protection?

I did exactly that with 8 batteries about 2 years ago for a 24V APC and they died about 6 months later :-( They were severly imbalanced, I suspect that the UPS' charging current is quite high on LA batteries and that the balance board cannot compensate the difference enough. Some cells leaked some black juice. Fortunately LiFePO4 batteries don't catch fire, but I was quite frustrated. These were no-name 32700 batteries. I'm going to retry with some LiitoKala, K2 or A123 and active balancers (1.2A, no longer the 50-60mA of passive ones). Also one thing is that the charge voltage for LA is slightly off for LiFePO4. Mine delivers 27.2V for 8 cells, or 3.4V per cell, that's 93% of the optimal voltage. The battery will be less charged, but on the other hand it will live much longer. I measured the cut-off at 22.00V or 2.75V/cell which is precisely where most cells are almost depleted so that should be OK. I calculated that in the volume of 2 12V/7Ah LA batteries or 168Wh, I could stuff up to 530Wh in LiFePO4, that's a huge gain. Anyway, thank you for posting this because I thought that I should document my project to encourage others to do the same, so with you doing it I have nothing to do anymore 🙂

Is this still working i m planning to make 8 cell each battery or just 24 volt ,outside battery