If your Nook Simple Touch won’t power on, or is displaying a question mark (?) on its battery indicator, I have a four things to try. But before you go to the trouble of disassembly, try charging the device with a different charger. Some chargers fit more tightly than others, and as devices like these age, they can get picky about their chargers.
If a charger change doesn’t give you an easy fix, the next step is to disassemble it, unplug the battery, wait a good 30 seconds, then plug it back in and reassemble.
You’ll need a very small slotted screwdriver or another sharp and semi-flat object, and a T5 Torx screwdriver.