First, let’s discuss the term 18650. This is not an arbitrary number in regards to batteries, it has a specific meaning. The first two numbers refer to the diameter on the battery in millimeters. The next two numbers refer to the length of the battery and the final number refers to the shape of the battery. In this case:
- 18mm Diameter
- 65mm Length
- 0 Shape (Circular)
18650 Batteries also come available with two different types of tops. This is the positive terminal of the battery and is referred to as either a “flat top” or “button top” battery cell.
You should always know which type of battery your device requires as a button top will take up more space than a flat top battery would.
Lastly, lets discuss the term mAh and what it stands for. This is an abbreviation for milliamp hour. When referring to 18650 rechargeable batteries, the mAh rating is the capacity or strength of the battery. The higher the mAh, the longer the battery will last between charges. This comes at a price as higher capacity (mAh) batteries have a lower CDR current rating so keep this in mind before just choosing the highest mAh battery.
- Flat Top – The positive end of the battery is a flat surface.
- Button Top – The positive end of battery is protruding.
This is the minimum capacity of the battery.
Capacity is measured by mAh (Milliamp Hours).
mAh is a unit for measuring electrical power over time.
A higher mAh rating means the (fully-charged) battery can power a device that consumes more power and/or for a longer amount of time before becoming depleted and needing to be re-charged
Continuous Discharge Rating
The maximum current at which the battery can be discharged continuously without damaging the battery or reducing its capacity as defined by the manufacturer.
Pulse Discharge Rating
The maximum current at which the battery can be discharged for a short period of time without damaging the battery or reducing its capacity as defined by the manufacturer.
A value assigned for classification purposes. Operation may actually be possible within a range, and the nominal voltage is often the midpoint of that range.
Protected batteries have a small electronic circuit integrated into the cell packaging. This circuit protects the battery against common dangers, such as overcharge, over discharge, short circuit/over current, and temperature. Please keep in mind a protected battery will be slightly longer do to the integrated circuit.