Since we're on the discussion of batteries for flashlights, everyone needs to be careful of lithium batteries. If you buy lithium batteries for use with lights or optics, make sure to only use batteries made in the US, and batteries made for use with the gear you're using. There are numerous incidents of Pakistani and Chinese made lithium batteries spontaneously combusting inside of weaponlights and optics. They are poorly built, and do not have circuit designs that will protect against overheating or shorting.
In addition to this, light and optic manufacturers have stated that you should not use photo lithium batteries in their products. Photo lithium batteries have a different cycling and discharge rate (or some kind of issue similar to that) that is designed for surges of current. Weapon light batteries like those from SureFire and Streamlight are designed for constant and consistent power output.
Besides this, photo lithium and normal lithium batteries are expensive. Why buy them when you can buy SF or Streamlight batteries IN BULK for a lot less?
Also, when you are storing lithium batteries, do not allow them to move around loosely. They should be in a container or compartment that prevents them from moving around. This is another cause of batteries catching on fire.