My UPS (battery backup, not parcel service) tells me I need a new battery.
Not in the beepy, blinky way that I would expect. Or in the "I ain't gonna work no more" way when the batteries die. More in the slightly excessive charging voltage causes the fan to turn on to prevent theoretical overheating, and turns my quiet apartment into My Own Private Tornado.
It's still functional... the fan is a safety precaution. The fan immediately turns off when the battery is disconnected, so it's the battery and not some other failure.
But I can't think with that much noise, much less sleep. So no PC or file server for a few days while the new UPS battery ships.
$80 to replace the battery vs $180 for the replacement model.
RetailMeNot shaved 12% off the cost, which offset the shipping & taxes. I stuck with my existing model, though the new model (Back-UPS Pro 1500) also supports an additional external battery pack for doubling the runtime. For not quite twice the price.