“Kindle’s wireless signal uses low power while in sleep mode so that your subscriptions can download overnight. If you are in a low coverage area, this could cause the device to use more battery power as it continually tries to maintain a signal. Unless you are subscribed to periodicals that you want to receive overnight, we recommend turning wireless off (Press the Menu button and select “Turn Wireless Off” of the menu options) before leaving the device in sleep mode. This will further conserve battery power.”
So, no subsciptions, no wireless!
Also, the Kindle battery does NOT need to be drained before recharging. It doesn’t have the memory effect.