If you are looking for maximum reliability, the Armytek 21700 Lithium-ion batteries are an excellent solution not only for Armytek LED flashlights but also for other devices requiring 21700 type batteries.
The Armytek "protected" 21700 Lithium-ion batteries feature triple protection against deep discharge, short circuit, and overcharging. Their stainless steel design is more resistant to impacts, and the cooling vents effectively prevent overheating.