Why Battery Rated in Ah (Ampere hour)

Why Battery rated in Ah (Ampere hour) not in VA.

Battery stores charge in the form of chemical energy and then converts it into electrical energy to utilize for a specific time. The amount of available charge is the capacity of a cell or battery which may be expressed in Ah (Ampere-hour). Moreover, in a charged battery, the numbers of molecules are limited to create a flow of electron in electric circuits, so, there must be a limited number of electrons in a cell/battery which they motivate through a circuit to fully discharge. Now we have the option to rate the battery capacity in the Number of flowing electrons for a specific time, but, it would be a headache because there are a vast number of electrons in it.

Mobile Battery

So we have another option (1C (Coulomb) = 6.25 x 10ˆ18 electrons, or 6,250,000,000,000,000,000 electrons. In addition, 1A (Ampere) = 1 coulomb of electrons per second and, 1h = 3600 Seconds
Therefore;

   1Ah = (1A) x (3600s) = (C/s) x (3600s) = 3600 C.

    ∴ A (1 Ampere) = 1 Coulomb per second = C/s

The amp-hour is a unit of battery energy capacity, equal to the amount of continuous current multiplied by the discharge time, that a battery can supply before exhausting its internal store of chemical energy.

A battery with a capacity of 1 amp-hour should be able to continuously supply a current of 1 amp to a load for exactly 1 hour, or 2 amps for 1/2 hour, or 1/3 amp for 3 hours, etc., before becoming completely discharged. In an ideal battery, this relationship between continuous current and discharge time is stable and absolute, but real batteries don’t behave exactly as this simple linear formula would indicate.

Therefore, when amp-hour capacity is given for a battery, it is specified at either a given current, given time, or assumed to be rated for a time period of 8 hours.

Approximate amp-hour capacities of some common batteries are given here:

• Typical automotive battery: 70 amp-hours @ 3.5 A (secondary cell)

• D-size carbon-zinc battery: 4.5 amp-hours @ 100 mA (primary cell)

• 9 volt carbon-zinc battery: 400 milliamp-hours @ 8 mA (primary cell)