**mAh vs Wh**

In the modern world hand held or portable devices are very popular and common. These devices are powered by batteries and draw little current and designed to consume minimal energy. When parameters of these batteries are considered, the values are small and hence smaller units are required to express them. The mAh and Wh are two such units.

**What is milli Ampere hour (mAh)?**

Ampere hour is a unit of electric charge. Milli Ampere hour is one thousandth of an Ampere hour. Ampere hour states that if an electric device consumes/supply 1 Ampere of current over a period of an hour (uninterruptedly) the charge passed through is 3600 Coulombs. Therefore, one milli-Ampere hour is 3.6 Coulombs.

The definition of current itself is the key concept in this unit.

*Current ( I ) = (charge flow)/time = ΔQ/Δt*

It can be rearranged as ΔQ=I×Δt. Hence the product of time and current gives the charge passed within the time duration Δt.

The unit milli Ampere hours are often used in measurements of electrochemical systems. In electrical batteries, such as the ones used in laptops and mobile phones, the mAh is mentioned. .

**What is Watt hour (Wh)?**

Watt hour is a measure of energy. Watt hour is the amount of energy consumed or generated by an electric device if it is operated uninterruptedly with a power of 1 watt for a period of an hour. It is equal to 3600 joules. Often watt hour is small to denote the energy usage/generation of an electric system; therefore, higher order units are used in those systems. The energy in power mains is always counted using these units. Power station outputs are often given in megawatt hours (MWh) while domestic electricity is recorded in kilo watt hours (kWh). [1kWh = 1000Wh = 3.6 MJ (mega joules) and 1 MWh = 1000000 Wh = 3.6 GJ (Giga joules)]

The definition of power is the key concept in defining this unit.

*Power ( P ) = (Energy Used)/time = ΔE/Δt*

Above expression can be rearranged as ΔE=P× Δt . It implicates that the product of the power and time gives the energy consumed or generated during the time interval Δt.

Devices like batteries gives relatively low power and hence watt hour (Wh) is used as a unit in batteries.

**What is the difference between mAh and Wh?**

• mAh (milli Ampere hour) is a unit of charge capacity or storage while Wh (Watt hour) is a unit of energy amount and storage.

• Both are small scaled units and used on batteries often.

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