A replacement for the popular CR123A lithium primary cell, the Trustfire 16340 (RCR123) rechargeable battery will save you money every time you recharge it and you won't keep throwing batteries away every hour or so. (Yeah, some people do that)

The protection circuit inside this lithium battery guards against over-charging and over-discharging, both of which are lethal to an unprotected cell.  The length may be 1-2mm longer than a lithium primary battery due to the added circuitry, but this poses no problem except in the rarest and tiniest of flashlights that have no tension spring.

Try these premium batteries in your flashlight and you will never purchase another primary/disposable battery again.

The earth thanks you for caring.

Note:
Never use unprotected 16340/RCR123 lithium ion batteries!  The cost difference is too small and the risk of property destruction and personal injury is too great.

As with all lithium batteries, use extreme caution with charging, use and disposal.