reply to stephiso
Re: Treadmill start = modem crash (interference) All but the oldest of APC UPSes have easily-replaceable batteries; most other brands are built similarly. Even the old ones can have their batteries changed, but it requires dismantling the case and maybe removing the circuit boards--I've got an 18-year-old-or-so APC "BackUPS Professional" (before model numbers) unit on its 5th battery, still going strong.
Most small (SOHO) units have single, non-spillable sealed-lead-acid batteries; originally gel cells, nowadays absorbed glass matt has taken over completely from gel. (Some motorcycles now use AGM batteries instead of flooded.) The only difference between that battery and one from Batteries Are Us is the UPS manufacturer's name on a sticker on the side.
The only hard part of finding a replacement battery is, usually, the "tabs" for UPS use are 1/4". The batteries that are easy to find are the ones for alarms and emergency lights, which often have 3/16" tabs. But, with that in mind, match up the voltage and get the amp-hour capacity near right and change that sucker out.
Or, for APC at least, you can find the Replacement Battery Cartridge number (RBC) and order one from any number of online shops like CDW, NCIX or NewEgg. (More convenient for the actual "packs" that are batteries tied together with the power connector.)