I've had a number of Fenix LED flashlights over the years but my two main ones now are the TK15 and the HL55. Both use a single cell 18650 LiIon battery that's a bit bigger than a AA batery but has 4X the energy of a NiMH AA battery. Both have variable power setting and at full power are way brighter than the legacy 4D cell Maglight yet at lower power can last for more than 20 hours.
I have one TK15 mounted with a quick disconnect to my AR15 and another I have for everyday flashlight purposes. The HL55 is a headlamp, also LED, that is useful when you need hands free lighting.
These are not cheap light and you're going to pay over $50 for them, but I don't go cheap on tools. You don't want to be out in the middle of nowhere at night with a flashlight that has sketchy controls.
Brian