I wasn't absolutely sure my problem was with the battery but I called Cyber Power's tech support and they suspected it was a battery issue. From the serial number he confirmed my CP1500PFCLCD was built in 2011 (I bought it in 2012) and that typically batteries last 3-5 years. He also confirmed my battery was the RB1280X2B model. Ordered the replacement battery on Amazon (thanks to other reviewers for flagging there are two battery models), it arrived the next day and took 10 minutes to install. Hardest part was getting the front panel off (after removing two screws the front panel slides down and then off). Installs very simply and works perfectly. Very pleased with this product.