Fantastic unit, with a fatal flaw. Even when plugged in to 110v, the unit often (more than once per day) believes there's no power, and goes into battery mode. Sometimes, it recovers after a few minutes. Other time, it drains its whole battery, and turns off! As a result, the unit has drastically lowered the reliability of power availability - precisely the opposite of what it is intended to do.I bought two of these units from Amazon, and will return them. I have since bought an APC XS-1500 which has less features, but works like a charm.I spoke to Xantrex technical support, but they had no solution other than "sorry, please return them and try to get another one from a different batch date". Mine say they were built May 7 2007.