Hello everyone I'm new here but here goes. I recently purchased 4 apc 1300s. I want to put lithium ion batteries in then but I need to either charge them separately. And thus deactivate the ups charger or boost it to 29.4v can anyone help me with this Please. I have limited knowledge, but the boards are labeled pretty well. I can not find any schematics.

 

Have you checked the charging voltage of the unmodified UPS systems? That is, the open circuit voltage when they are powered up , and both with the batteries connected and not connected?
And what is the motivation for changing the battery type? I am not familiar with that particular model of UPS, although APC has been producing UPS systems for many years. So I am really wondering why change battery types.
AND, you will not be able to find a circuit schematic because they do not ever expect these units to be serviced, except for battery replacements.