21700 Lithium-ion batteries: large batteries with lots of capacity
The 21700 batteries are known for their amazing capacity. Most batteries have a capacity of no less than 5000 mAh. As such your light will burn longer, but also brighter. The 21700 batteries are a little bigger than its brothers. So do make sure your flashlight can handle a 21700 battery. As is the case with all Lithium-ion batteries the 21700 batteries will also last longer if you charge and use them on a regular basis.