What is mAh?
This is the abbreviation of miliamperes per hour, the unit that measures the electric power over time, used mainly in batteries.
An example is a battery with 2000 mAh means that it could power a device during 20 hours if the device draws 100 per hour.
There is no relation between the mAh of a battery and its lifetime, however the concept measures how long the battery will transfer electricity to a specific device, based on its electricity consumption.
It is important to take into consideration external factors like environment temperature, the age of the battery and more, so it is advisable to always calculate values with margins of mistake.