LPT: if your phone runs out of battery, you can "charge" it using your body heat

This has saved me numerous times before when I was looking at maps or I needed to do something and my phone died at 30%.

If it runs out of battery, take off the case if you have one and hold it flat between the palms of your hands. Wait like this for 2-3 minutes and you should be able to turn on your phone. It will still be very low on charge though so do whatever you need to do quickly.

This also works for double- or triple-A batteries.