A GE-NXV2 system came with our new residence which we moved into 3 years ago. So at exactly the 3 year mark the power led on each keypad started to blink green and the panel service message indicated "control low battery". So I replaced the stand by battery, A-XCELL 1240, with a new battery, UMB 1250 . Unfortunately, each keypad is still in the same state with the power led blinking green. Can one of you experts please point out what else might be wrong?