I've got a roughly 17yo APC Back-UPS RS 1500VA that out of the blue started beeping with nothing connected to it but a strip of led lights and a couple of chargers for a flashlight and some tools. None of which were being used. I turned it off then back on hoping it would start charging the battery but no love. It went straight to battery and stayed there until the battery was virtually dead, beeping away. So I grabbed my laptop and plugged it in to see what was going on but it wont even allow me to run a self test. Now if I turn it off, the battery will charge back up normally but as soon as I turn the unit back on it goes right back to battery( even with nothing plugged into it). The only thing I could think of was that maybe a relay has gone bad but I'm grasping at straws tbh. Prior to this I replaced the batteries about a year ago and it's been running fine. Anyone have an idea what may be wrong with my old gray mare?