If you're looking for maximum reliability, the Armytek 21700 Lithium-ion battery is a great solution not only for your Armytek LED lights, but also for other devices that require the 21700.
ArmyTek "protected" 21700 Lithium-ion batteries have triple protection: against deep discharge, short circuit and overcharge. Their stainless steel design is more resistant to shocks, and their cooling vents effectively protect against overheating.