3.7 battery 18650 is a lithium-ion cell classified by its 18mm x 65mm size, which is slightly larger than a AA battery. They’re often used in flashlights, laptops, and high-drain devices due to their superior capacity and discharge rates. 18650s come in both flat and button top styles, and usually boast 300-500 charge cycles. Lithium batteries are a great option for today’s high-end electronics as these cells typically have higher capacities than their alkaline counterparts. Although rechargeable batteries tend to cost a little more than standard alkaline batteries up front, these costs have reigned in because you won’t need to replace rechargeable batteries nearly as often as alkaline cells.