I just noticed that this K2 (while still plugged into the USB charger) is now showing the kindle GUI framework. It has 25 books on it. The settings menu shows that it is still registered, but the previous owner had the radio turned off, so perhaps it was derigistered at amazon. I will make a backup copy of the userstore partition before I turn the radio on...
Yay! It works! Now to unplug it from the charger to see if that battery is acceptable to the kindle. I will test it, then do a restart from the settings menu, and test it again...
Umm... the LED only stayed on (amber) a few seconds after unplugging it -- BUT it did NOT come on after replugging the power, until I jiggled the battery module. Yeah, it flexes too much wihout extra support.
VERY carefully (so as not to wiggle the battery, on battery power only (no USB cable): "menu / settings / menu / restart". It restarted. It displayed the GUI framework (showing all those books), but with a popup warning that my battery is running low and I should connect it to a charger.
YES! My "battery surgery" was successful!
Any old cheap LiPo battery CAN impersonate an authentic amazon battery (with a "brain" transplant -- i.e. that little circuit board harvested from the old dead battery).
Enjoy!
EDIT: Though I wonder if this tiny little 500mAh battery can last long, especially when it has been unused and uncharged for a couple of years... ESPECIALLY if I use it to play videos with my kindle video player, eh? But for just book reading? Probably a lot longer than using my smartphone to read books, for sure...