What is Amp Hour or Ah?

Frequently Asked Questions About Braille Battery and its Products
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What is Amp Hour or Ah?

Postby admin » Tue Nov 08, 2011 4:14 pm

If a battery was a motor, cranking amps refer to the horsepower of the engine, whereas AH (amp hours) are the amount of fuel in the tank. To test the amount of “fuel” in the tank, the battery is tested to determine the amount of amperage available when discharged evenly over a 20 hour period. The amp hour rating is cumulative, so in order to know how many constant amps the battery will output for 20 hours, you have to divide the amp hour rating by 20. Example: If a battery has an amp hour rating of 75, dividing by 20 equals 3.75. That battery can carry a 3.75 amp load for 20 hours before dropping to 10.5 volts. A battery with an amp hour rating of 55 will carry a 2.75 amp load for 20 hours before dropping to 10.5 volts.
Higher ratings do not necessarily reflect how fast current can be drawn, rather, how long a current can be drawn. For example a 20Ah battery will sustain a 1-amp draw for approximately 20 hours before dropping to a voltage level that is considered discharged. A 40Ah battery will sustain an 8-Amp draw (or load) for approximately five hours. Capacity is influenced by other factors such as temperature, depth of discharge and speed of discharge.

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