Lithium replacement batteries. Are they compatible

[rossbaker.com]

Lithium replacement batteries

Are they compatible with APC BackUPS XS 1500

[Teken]

Short Answer: No

Long Answer: Depends on what type of internal BMS is inside the cell. Very few of the Amazon listed LiFePO4 cells are either (HR) High Rate discharge or do not support series / parallel configurations. 

The major fault you’ll see when there is a internal BMS inside is it won’t turn back on if and when the system is fully depleted! 🤦‍♂️

Depending upon what model APC UPS you have and it’s designed topology. The unit will NOT turn on if it detects a zero volt / low voltage condition! ☝️

So what people have done is ghetto wired the BMS to jump start it with external charging leads / ports. Once the BMS has been (turned on) and the cell is at the expected voltage the UPS will than allow you to power on the system.

As you see it takes a lot of trial and error to find a so called drop in replacement LiFePO4 battery. 

I haven’t even mentioned the charging / float voltage is not the same as a lead acid battery. 🤣

NOTE: All of the above would certainly void any warranty in place. The risk of an explosion is extremely high. A LiFePO4 fire is extremely hard to put out when present. As it relates to any home owner’s insurance policy against fire - None!