I was reading in the hot tub and accidentally dunked my Kindle (named 'Kenny' for reasons that won't be enumerated here). After a week in rice, I tried to turn him on, and I found that I could get him to work only when plugged in and charging, but the charge indicator never got above 2%. Hoping that replacing the battery would revive him, I went to the internet for help and found Ifixit.
Getting the back off was a little trickier than indicated - the tolerances were just so tight that it was hard to work the edge of the tool into the crevice to get the first latch free. Changing the battery was a snap after that. It didn't fix everything - he still shuts off instead of just going to sleep when no in use, but he holds a charge and I was able to finish the book I was reading in the hot tub,
Specify that the tools come included in the price of the battery - I bought some separately, so now I have spares! And, oh yeah, don't fall asleep while reading on your Kindle in the hot tub!