APC 1500VA UPS battery backup SUA1500RM2U repair and partial  

Let me point a couple of things: 1) Batteries in series setup MUST be of equal type and installed at the same SOC (state of charge). Imagine if one is 3/4 charged and others fully charged. The system will try to charge the pack to complete the less charged one and overcharge the other ones. For the parallel setup, they'll try to immediately equalize tension with high currents. Always test if all equal type batteries are at the same rest tension. If not, just charge each one to fully charged individually with a 12V charger. 2) Always unplug the negative pole first and plug it back last when dealing with lead acid batteries. Lowers the chance of producing an internal spark igniting the hydrogen produced when charging.

Amazing...every second was very interesting and I learned a lot. You made the process seem doable... with tips for safety. Thank you. Gifted!

Thanks for this. You would not belive how impossible it is to get the wriring diagram for these dang things!

this a 24V battery pack. you have two fuses, one for each series; i think that only the 3000VA model has a 48V battery pack

I was hoping maybe you had some advice the 4 batteries that I have for the apc have all swelled and were unable to take the packs out any tips?

Use aluminum foil to discharge Caps - or look on the PCB for a 'discharge' jumper - good units sometimes have one for safety

The batteries are so expensive because of companies that obey OSHA rules. I have to replace (rebuild) some battery packs for our UPS's at a remote site and I have to get electricians involved because the battery packs are over 50v (72v). With replacement battery packs, I'd still need an electrician, but it would be 5 min.

Buy batteries and connect them yourself - $80 Buy a battery pack - $200-300 So the extra $120+ that they charge is just for for assembling the batteries in a pack. Nice.