As Ric said, batteries can be purchased cheap, but not thru the UPS manufacturer(most are Universal brand name or can be subbed by them). The thing to remember is that the batteries in the UPS need to be cycled for them to last. Once a month, unplug the UPS from the source and let it run for several minutes, then plug it back in. The batteries will last much longer. This also tests the functionality of the system, instead of finding out it is NFG when the power goes out, or a brownout causes problems.
