Before getting into the different chemical constructions of the different types of batteries, it’s important to have some general knowledge about how batteries work since they are measured a bit differently than other electrical appliances.
Capacity: Capacity refers to the amount of charge a battery holds. It is measured in milliamp-hours (mAh), or amp-hours (aH). A battery’s mAh is normally listed on the side of the battery, and you can figure out how long you can expect the battery to last using this simple equation:
Amp Hours (aH) / Amps (A) = Hours (H)
For example, a 2,500 mAh AA alkaline battery could power a device that draws 250 mA of current for 10 hours. However, if the load draws 25 mA of current, the battery will last 100 hours. The overall life of your battery depends on what you use it for, but a general rule of thumb is that the higher mAh a battery has, the longer it will retain its energy.