APC Smart UPS 1500 random shutoff

Hi I've got an APC Smart UPS 1500 that's acting very strange. It'll look fine, all lights green, tests ok. Then it'll randomly shutoff. I'll hit the test/power button to bring it back up, it'll start, do the startup test, and go back to it's normal state with all LEDs green. The charge is full and the load is only half. I can even unplug it from the wall and it'll discharge like normal. Anyone ever seen these behave this way? My guess is it's toast.