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A current flow for one hour measured in amperes (amps). Abbreviated "Ah" and commonly called "amp-hour," it is widely used to rate how long it takes for a battery to discharge. For smaller batteries, a milliampere-hour (mAh) rating is used. For example, a 500 mAh battery means it will release 500 milliamps of current at a specific voltage for one hour before it is discharged. See ampere.

Amp-Hours and Watt-Hours
Batteries can be rated in amp-hours (Ah) or watt-hours (Wh) as shown in these examples for a digital camera. The bottom battery is equivalent to 3.3 Wh, while the top battery is equivalent to 667 mAh.


A measurement of electrical current in a circuit, commonly called an "amp." Contrast with "volts," which is a measure of force, or pressure, behind the current. Multiplying amps times volts derives "watts," the total measurement of power. In electrical equations such as Ohm's Law, the symbol for ampere is "I" (see ohm).

One ampere is 6,280,000,000,000,000,000 (6.28 x 1018) electrons passing by the point of measurement in one second. See ampere-hour, volt and watt.

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ampamplitude modulation
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amp-hourAMPS modem

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