Yeah, when my NGG started not booting in the middle of last year, I eventually tracked it down to a bad MPU board due to battery corrosion. The batteries only get used when the machine is powered off. The longer your machine is powered off, the more often you’ll need to change the batteries. That was new information to me at the time.
Battery corrosion is an insidious issue that’s difficult to immediately diagnose and it starts causing all sorts of crazy seemingly unrelated issues, when in fact, they’re all related. The machine usually starts exhibiting some odd error/behavior as the corrosion expands and results in an eventual total shutdown. My battery corrosion was not visible until I pulled the board and inspected the back of the board.
I wound up replacing the board (w/ ASIC chip), transferred over the processor, ROM, and security chips and it’s been solid ever since. On the new board I installed the external battery compartment. I now use lithium AA batteries (not supposed to ever leak), not alkaline.