I've got a UPS that charges its batteries with 84 V 1.5 A (6S1P SLAs). I want to replace the batteries with li-ion 20S2P. I'll use an external charger to charge them in cases of prolonged power-outages, but mainly they would be charged by the UPS.
Just to by safe instead of a simple BMS, I can install a smart BMS (Ant-BMS or Daly) and set it up to function between 3.4-4.1 V in cells. Which still would give me ~90% of capacity.
The question is - is it safe? The UPS was made for lead-acid, so it definitely has float voltage. Plus it may have a equalization mode(unlikely). But the BMS should be able to cut off both float and equalization, right? I can reduce the BMS's upper voltage for cells even more (4.05 instead of 4.1 V), which would definitely be lower than (13.5-13.8 V)*6 float voltage of the UPS's original batteries.
I understand that it would be better to get a li-ion UPS. But money is tight now.
If my setup would reduce life of the batteries, even by half - I don't mind. What I need is - for it to work reliably and safely for the next 2-3 years with semi-regular power outages that sometimes exceed 48h.