Dimensions
Example: 18650
The number references the dimensions of the battery.
Although these appear to be one number, they are broken down into two parts. The first 2 numbers and the last 3 numbers.
18 – diameter of battery in millimeters (mm).
650 – length of battery in millimeters (mm).
Milli Amp Hours (mAh)
Example: 2100 mAh
The number references the battery lifespan.
The larger the number, the longer the battery will last when used in a device compared to a battery with a lower mAh.
The lifespan is directly related to the load or Ohms of the coils that your battery is giving its power to.
Degradation of your battery increases as your coil Ohms drop.
Example: A 2100 mAh battery with a 2.4 Ohm coil will last longer than a 2100 mAh battery with a 1.5 Ohm coil.
Standard Operating Voltage
Voltage your battery operates most efficiently at its maximum voltage.
Li-ion batteries voltage spikes when fully charged to around 4.2V but drops quickly and will sit at the 3.7V until it has a low charge.
Although it varies dramatically between chargers and batteries, most cannot recharge a battery once it has gone below 2.2V.
With standard 18000 series batteries, your standard operating voltage will always be 3.7V.
Charging Safety
Be sure to wait until your battery is fully charged to remove it from its charger.
A battery that is not fully charged will eventually lose power and overall lifespan due to dead cells.
By not charging your battery fully you will not be at 4.2V and therefore, will not get as much time or power.
90% of battery failures occur when charging and in most cases is due to improper placement (positive to positive, negative to negative), or using improper or poor quality chargers.