Neato Botvac D80 issue.

I own 2 of these units (identical). By swapping a couple parts I have determined that the battery, and charger base are not the problem. Bad unit has no power at all. If I put it on the base to charge, Home button lights up green, tells me to turn the switch on (it’s already turned on, but I press ok anyways). Home button turns to amber (slow blink to indicate charging has started). After between 10-30 seconds, it changes to rapid amber blinking on home button and after about 3 seconds it shuts down, reboots and starts the process all over. Ideas?