This is something that has had me stumped for over a year. I have 3 APC SmartUPS 3000's and a few non APC units in my server room. Each unit has it's own dedicated connection to the breaker panel.
It seems that I am having to replace the batteries in these units once every 4 months or so. We rarely ever have a power outage, as in not a single outage since the last time I replaced the batteries. I thought maybe it was bad line voltage, so I logged the UPS's output and I did not have a single sag or over-voltage scenario in those 4 months.
Maybe the lines were wired wrong? I tested them and traced them back to the panel and they all checked out.
I decided that the only possibility was that the replacement batteries I was using were not that great (Duracell). I proceeded to buy two brand new APC UPS units with new APC batteries of course, and after four months they were both dead.
The units never register an event in which they switch to battery power, they just simply report bad batteries after 4-6 months. This is a recurring problem that affects multiple units of different models and different brands of batteries. I have no clue whats going on here, I've had electricians and the provider test for various things, and it always comes back clean.
At this point I can only think of something being wrong at the provider level (bad transformer?), but usually that will cause voltage issues. I have also heard of people having phase shifting problems, but I have single phase power, so I am not sure if that is relevant or not.
Note: I used to be an electrical engineer and I have a fairly high level of understanding on how this is supposed to work. So you don't have to dumb down your answers :)