# 18650 Battery | | An **18650 battery** or 1865 cell is a cylindrical lithium-ion battery common in electronic devices. The batteries measure 18 mm (0.71 in) in diameter by 65 mm (2.56 in) in length, giving them the name 18650. The battery is 3.7 volts. | |-|-| | | wikipedia:: [18650 battery](https://en.wikipedia.org/wiki/18650_battery) | [[Lithium ion battery]] Called 18650 because they are 18mm by 65mm 3.7 [[Voltage|Volt]]s between 1800mAh and 3500mAh (mili-amp-hours). now commonly used in power tools, electric bicycles, laptops, and electric vehicles.[5] and [[Codex/Tech/Making]] 18650 batteries are more commonly used in packs, where a BMS (Battery Management System) is required, especially once cells age and perform differently. BMS boards balance the voltage of cells in series and protect against over- and under-discharge. We also recommend you stick with high quality “brand name” 18650s. Many knock off, no-name brands lie about high mAh (capacity). The average 18650 battery charge time is about 4 hours. Charge time can vary with amperage and voltage of the charger and the battery type. ## Versions/sizes Devices only work with certain sizes... - Unprotected - can be overcharged and burst and potentially cause a fire unless there are specific electronics to protect the battery. The popular LG HG2 and INR and Samsung 25r and 35e are UNPROTECTED batteries, only use them in a device designed to use unprotected 18650s. - Protected - include a protection circuit that stops the cell from being overcharged. - Flat top - The battery's positive end is flat. - Button top - The battery's positive end is protruding. ## Overcharging > Protected battery doesn't mean you are free of concern > > The specific voltage of a working 18650 battery ranges from 3.2V to 4.2V > > The voltage limit setting of PCB is 3V ~ 4.35V. > > Unfortunately, this control system is not very precise. > > PCB doesn't stop charging until the voltage reaches 4.35V. But the peak voltage of the battery should be 4.2V. > > For the sake of longer battery life, don't leave it charging overnight. The advised charging time of one single 18650 cell in a typical charger is between 2 to 3 hours. ## Sources - [Everything You Need to Know About the 18650 Battery](https://commonsensehome.com/18650-battery/) - [Beginner's guide to 18650 battery with easy-to-understand illustration - SkyGenius Online](https://skygenius.cc/blogs/guides/beginners-guide-18650-battery)