Removing swollen batteries from, and servicing a 1500 VA APC UPS
Channel: FFcossag
Date: 2014-03-20

Practically all APC UPS units have very poor battery chargers; they only have one charging mode, and that's float charge at 13,8 - 14 V, which is far too high for float charging these kinds of batteries.

The result is that the batteries boil away the water in their electrolyte, at first causing irreparable corrosion of the lead plates, followed by swelling due to maintained high pressure in the long term, and destruction of the batteries as well as damage to the UPS case.

Whenever you replace the batteries in a black APC Smart-UPS, you should adjust the ADC and lower the float charging voltage. This will literally increase your battery lifetime by years. The downside to doing this is that it will take a much longer time (days) to saturate the batteries fully after a discharge; the last 5-10 % capacity will only be able to enter the battery at a very slow rate, but this is usually not a problem in normal operation, since you usually don't cycle your UPS batteries more than a few times a year, if that.