18650

The most popular format of lithium batteries is 18650 (diameter 18 mm, length 65 mm). It is widely used in flashlights, power tools, vape devices, household appliances, and automotive equipment. The typical lifespan is up to 500–1000 charge cycles.

These batteries are sensitive to deep discharge, overcharge, and charging at negative temperatures. Never carry them loose in your pocket without protective packaging, as a short circuit can be dangerous.

They may come with or without a protection board (PCB). The positive terminal can be flat-top or button-top. The maximum practical capacity of 18650 cells is around 3900 mAh.