Thread drift but still about UPS - I've replaced the single 12v battery in mine several times - they only seem to last a couple of years. The problem is that these days they don't keep the PC etc going for long even when new and fully charged.
Would there be any problem running a couple of large-cross section cables out of the UPS to a 12v automotive battery under the desk ("under the desk" isn't part of my query !), IOW replacing the small internal UPS battery with a much larger capacity external one ?