18650 battery basics

The 18650 battery looks a lot like a large version of the 1.5V AA alkaline battery cell. But, it’s chemical properties are very different.

I really like this charger.

Information not guaranteed to be accurate. Always consult the manufacturer datasheet/specifications.

Basic properties

  • The 18 stands for 18mm wide, while the 65 stands for 65mm long. Button tops are usually a tiny bit longer than the flat top versions, and may not fit in some holders. Many sources say that the 0 after 1865 indicates that the battery is cylindrical.
  • Lithium ion chemistry. A single li-ion cell (such as the 18650) is generally rated as being 3.6V. Most 18650 should never be charged above 4.2V and is best to not discharged below 3V, while never discharging below 2.5V. It’s best to remove the 18650 from the charger as soon as they are recharged if the charger doesn’t completely stop charging automatically.
  • Some 18650 have circuitry in them that will protect the battery (disconnect the chemistry from the circuit) if it is subjected to unsafe conditions.
  • Many 18650 batteries are fakes. They probably have li ion chemistry in them, but less than they should, or are repackaged batteries that have been heavily used/abused. You won’t get the performance that you expect, and they may be dangerous to use.


Comparing 4 18650 li ion battery pairs by analysis charging from 3 point 2 volts to 4 point 2 V

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