Dead Battery Hand Warmer
Alkaline batteries will usually stop being able to power your electronics long before they are empty. One way to use that last bit of energy is as a hand warmer.
Once your battery is mostly dead, use a 1 ohm resistor (or an equivalent length of wire with at least 1 ohm of resistance) to bridge the terminals. This will slowly drain out the last of the stored energy and release it as heat. This can make a very low powered hand warmer. It won't make a lot of heat, but every bit helps.
- Only use alkaline batteries. Never use other battery types. Lithium batteries can actually explode if they are discharged too quickly.
- Only do this with 1.5V batteries. Never use higher voltages such as 9V or 12V.
- Only do this with batteries that are mostly dead. If you use a fresh battery, It will release much more heat and could burn up the resistor and burn your hand. For new batteries you would need to use a 10 ohm resistor.