[Nook HD, HD+ Q&A, Help & Troubleshooting] nmyshkin:
Wow. This just gets weirder and worse(r). We've been running first CM 11 and then CM 12.1 on this HD for awhile and all was fine. Suddenly the battery indicator became wonky, dropping from 50-ish% to 1%, precipitating a shutdown unless the tablet was immediately plugged in. Then suddenly the battery indicator would return to normal and you could unplug the tablet.

Next, after running a backup on the CM 12.1 ROM the tablet started crashing during boot (the cyan android phase) UNLESS it was plugged in to the power supply (USB to computer is not sufficient). This, despite a good charge level on the battery. After a minute or so when the boot was complete, you could unplug the tablet and go on your way.

Today the screen flashing began. Makes the tablet completely unusable. Sometimes you can calm it down for awhile by connecting via USB to computer, sometimes not. This thing is freaking me out. I just recently took the tablet all the way back to stock and resintalled CM 12.1 from scratch, including building a new SD card from new files. Before someone asks, it's a class 4 card. I've always been fine with Class 10 or UHD cards when working with my Nook Tablet, but for some reason I decided to play it "safe" with the HD and hunted around for a lower class. Maybe a mistake?

Finally I took the tablet back to stock again today, completed the sign-in process to the old B&N account and everything is fine. No screen flashing, no funny business with the battery indicator, no problem booting without the power cable.

I just ordered a "new" (out of box) replacement for the tablet on ebay, but it doesn't seem like this is an actual hardware issue.

What scares me now is a potential repeat of this process with the new tablet. I've never had any experiences like this with my old Nook Tablet. I'm at a complete loss.

Help!

Edit: OK, we seem to have tracked down the general source of the screen flashing. The backup we have been restoring is from July 2017 so quite a few apps want updating. We noticed things would be fine for awhile and then the flashing would start. At one point "Unfortunately Google Play Services has stopped" kept popping up. I began to suspect either a bad or incompatible update was messing with the system. So...we did another restore of the same backup but immediately turned off auto-updates from the PlayStore. Three days later and no display flashing. One small victory.

Could the shutdown during the boot animation be caused by a corrupted file? I don't see how since it boots OK when plugged in, just not on battery, but I'm willing to pursue any possibility.

Edit.Edit: Well, well.... We got a "new" open-box HD from ebay and I started working on it. I noticed in making new SD cards that one I had been working with was not properly set to 0x0C FAT32 LBA. I fixed that. This time the tablet will boot into the OS without being plugged in! Yay! Still have to test that on the old one after I finish building a duplicate system.

I'm restoring apps and everything is fine until suddenly the flashing starts up again. But now I know when it did. The offender seems to be the 0.15 version of Lithium Epub reader. I managed to uninstall that via ADB (with screen flashing you can't do much with the tablet except ADB). Voila, no more screen flashing. I found a copy of version 0.13 and installed that. No flashing screen. Needless to say I've set the app to

not

auto-update.

Edit.Edit.Edit: Well, $40 later we now have a second Nook HD and both are running fine. Hard to imagine that the goof that somehow happened to the SD card would manifest as only being able to complete boot when plugged in, but that must be it. Returning to stock (tried that...) and reflashing with the newly prepared SD card did the trick. Moral: sweat the small stuff.