Karoo 2 won't power up

This Karoo 2 is several years old and has worked well.  Yesterday it would power up only enough to display the Hammerhead text, then immediately back off.  Left it on the charger all night and it will not power up at all. It does not light up when the charging cable is plugged in.

Removed the coin slotted cap on the back that looks like a battery access.  Not a battery.  A metal cover will open.  Looks like access to some test points.  Did not mess with it any further.

Removed two torx screws on bottom next to the charger port.  Did not recognize anything else to provide to access the battery or open anything else.

Is there anything I can do to determine the problem?  Battery?

Thank you for your time.