How to calculate the power of the battery?

A battery is an energy storage component, without power, it has a rated capacity, which is the time it can discharge.

For example, a 3000mAH battery with a rated voltage of 5V supplies power to a consumer device with a power consumption of 2.5W and a voltage of 5V. Its theoretical usage time is:

1 Most direct algorithm: First obtain the current of the electrical device, and then divide the battery capacity by the current of the electrical device to obtain the usable time.

I=P/U=>2.5w/5v=>0.5 A=>500MA   3000/500=6 hours

2 By using the Coulomb algorithm of charge quantity:

C=IS=>3A * 3600s=>10800c Coulomb (charge quantity)

10800c * 5v=54000w electrical energy     54000w/2.5w=21600/3600s=6h