You could try this handygran. Hope it helps.
If the battery isn’t too far gone, here’s how to revive it:
1. Plug the device into the Kindle A/C adapter (not your computer) and let it charge for a few hours. Be sure the charging light is lit — sometimes a drained Kindle will stop charging a few seconds after you plug it in. Unplug and replug until the light stays on steadily, then leave it alone. Most of the time you’ll come back to a restored Kindle. If not, go on to step 2.
2. If you still see the same Critical Battery screen after charging, unplug the USB cord, then hold the power slide to the right for at least 20 seconds.
3. Release the power slide, then immediately press and hold the Home key for another 30 – 45 seconds.
4. Once the Kindle’s screen begins to flash, release the Home key. The eReader will boot to recovery mode. To continue, press and hold the R key until the screen flashes again.
5. After the device is finished rebooting, you may see the Critical Battery screen once more. If so, plug in the USB cord and wait for the Kindle to return to the Home screen.