Hi again I have a APC/UPS the batteries in these units are suposto be changed everey 3-4 years. As they dry out from being contantly charged they are a sealed unit so you can not top them up or anything like that. A set of new batteries costs me about $120.00 every 4 years, I think that is a good deal as I get mine from the battery man. my unit will power my return pump for about 2 days. or if I have my heater on it also I can get about 6.5 hours out of it.

Bill