Question

I cant understand what does 4000 mAh mean and what's the meaning of 3 volt?​

Answer 1

The symbol mAh means milliampere hour. This is a unit of electric charge, and it's the most common way to express the capacity of small batteries. Bigger batteries are labeled in ampere hours.

The term voltage in a battery refers to the difference in electric potential between the positive and negative terminals of a battery.

Batteries range in voltage from a few hundreds of a volt to many hundreds of volts, depending on both the size of the battery and the materials from which it is made.