What is an Amp hour?
Ampere hour (Ah) is a unit of measurement that is independent of power and is quite different from Ampere. Amps are to describe ampere hours, but they are different units of measurement.
Amp hours describe the charging capacity of a battery.
For example, a 12V Lithium battery rated at 80AH will be able to supply 20 amp for 4 hours before dying. If the current draw increase to 40 amps, the battery will only last 2 hours.
Now this is under ideal conditions, perfect temperature, no vibration and stable power. We say capable charging because in the real world, you’ll never meet those ideal conditions. There are energy losses associated with internal resistance, etc. If you were to put a steady 90 amp load on the battery above, it obviously wouldn’t last anywhere near the 30 minutes suggested by its AH rating. If the the battery is damage, it is likely to overheat, die and no longer hold a charge. Just think of amp hours as a way of knowing that one battery has more charge than another. You’ll be able to use your drills, circular saws and puzzles longer before the battery runs out.
How to calculate the Ah of a lithium battery?
An ampere hour combines the amount of current with the time taken for a battery to completely discharge. A simple way to look at it is: 1 ampere of current flowing for one hour. During the hour, the amount of charge transferred in is 3,600 coulombs (ampere-seconds).
Mathematically, Ah is represent as the following:
Amp hour (Ah) = Current (I) x Discharge time (T)
The calculation involved in determining the ampere hour rating can be understood with the following example — consider a battery that pulls 60 amps (A), which is discharged in 30 minutes:
Current = 60 A
Discharge time = 30 mins (0.5 hours)
Ampere hour = 60 x 0.5 or 30 Ah for 1 hour
The following is another example:
Current = 10 A
Discharge time = 5 hours
Ampere hour = 10 x 5 or 50 Ah for 5 hours
The ampere hour rating are display on the battery. If the rating is not specified, it usually means that the battery is a starting battery that’s not designed to provide continuous power in ampere hours.
What is Watt hours on a battery?
(Wh) is an abbreviation for Watt-hour, and we always measure the capacity of any given battery in electrical applications. In simple terms, it describes a battery’s accumulated energy.
It is easy to determine the watt-hours of a lithium battery because it state in the case of the battery itself. All newer lithium-ion batteries have visible watt-hour ratings. If your battery is older and you cannot see the watt rating on the case, you can calculate it as (Volts by Amp-hours). You can also consider checking the product documentation sheet for the specifications of the battery. However, if it does not appear in any place on the document and you are still unable to calculate it, you can contact the manufacturer.