We had few days of rolling power outage that lasted in 2 hours blocks while they were working on grid. So I started to do research on how to extend a life of UPS batteries to last during these down times. And I found a simple solution.. Get a car battery and connect it to UPS. This is also good solution if you have old UPS that does not hold the charge. The car batteries are cheaper and larger Ah then UPS batteries (different technology).
What you need to get is good solid UPS that does not have batteries. Ebay is good source. What I would get is brand name UPS like APC. Also it needs to be at least 800 to 1000VAC (very important). A small or cheap UPS might have overhearing problems, read the link below. Do keep in mind that some UPS use one 12v battery and others have two 12v (24v), so you will need to get two car batteries and link them. The 50Ah to 60 Ah batteries are good starting point, they are big enough but not to big to over load UPS inverter.
These are standard lead-acid deep cycle batteries, meaning that they can and do release gas when discharging. For that reason, I have these batteries situated outside. To do this safely indoors, you need a well-ventilated room OR you need to use sealed batteries. Other alternative is to get longer cables (too long of cables will over heat).
My setup is APC UPS with 55 Ah. Remove old batteries and solder a longer wires to original wires going to UPS batteries (make sure you get large enough wire, proper gauge). Get 2 car batteries (lug) connectors from your car parts shop and place then at end of cables. Make sure you connect red cable to + and black cable to – sign on the car battery.
… pictures to come….
see my other post relating to Desulfator and procedure to bring life back to battery. Desulfator