Two hacks on batteries surfaced recently. One on AA battery and the other one on AAA battery.
Personal Finance Advice discovers all disposable cameras have a battery (usually AA battery) in them which are there for powering the flash. Most of the time, when you take your disposable camera to develop your firm, the store will open the camera, get the film and throw it away. So it is possible to ask those stores that develop firm to save those unused batteries for you.
— Why I Never Pay For AA Batteries
Axe Collector shows how you can rip those 9 volts battery apart and grab those battery cells inside and used as AAA batteries
— Why I Never Pay For “AAA” Batteries