My first computers taught me a lot about needing backup power solutions. I would spend a couple hours writing a program only to have a power glitch evaporate my efforts. I was lucky to have a computer that ran on 12V, so extending the power running the lights into the closet with the computer was not really difficult. My next PC had a traditional AC power supply which made things a little more complicated. I had already built a small UPS for the lights on the fireplace so it wasn’t difficult to build a bigger one that could also support the computer. (Just more money in parts.) Lightning struck a tree in my neighbors yard and that fried my home built UPS sitting the garage floor. I did not like the rather expensive UPS units in the stores, they all had an awfully short run time. It also didn’t make sense to purchase multiple UPS units because their batteries were a significant long term cost. I ended up buying two medium sized UPS units and wiring them to rather huge batteries. (I wasn’t worried about recharge times that would be several days.) There are too many variables that have to be taken into account and significant risks of modifying a consumer UPS unit to recommend it to anyone. (FYI, they are designed by cost concerns not the consumer’s needs. Most of them will approach terminal temperature by the time the battery is exhausted. So extending the battery yields dangerous amounts of heat and a possible fire… *Check it out on YouTube.)