Also, "round up the usual suspects".
One of these is to check to see if the Kindle's search indexing is having problems with one of the books. When this happens the processor runs full tilt until if finishes the indexing. When it can't finish it will run the battery down quickly, a few days to a week with a new battery and perhaps only a day with a aged lower capacity battery.
Do the following:
- Wait several hours after adding a book to the Kindle.
- Put the Kindle on the AC adapter or be certain the battery is fully charged
- Go to the Home screen
- Type some garbage characters (e.g. "qqzz", ...) that won't be in any book
- Select "Search"
When the screen appears reporting the search results it will list the number of un-indexed books, if any. If there are un-indexed books click on the number and see if it will list the books. If so, delete those books and test the Kindle for a few days. If battery life improves, add the deleted books one at a time over several days, repeating the above to see if the indexing goes correctly this time.
My K3 has chocked on books several times over the last 2+ years. I notice this when battery life seem to be extremely short. Deleting the book and reloading it has, so far, always worked to resolve the issue.
At 2+ years of daily use my battery life has dropped a bit. I've noticed that I need to charge every 2-3 weeks these days, when originally I could go 4-5 weeks between charges. This type of battery looses capacity after time and usage. Initially, this loss of capacity will be gradual but at some point toward the end of its usefullness its capacity will start to drop off very quickly. When that happens, you need a new one.