# mah

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ampere-hour Rechargeable batteries
Top: AA battery (2500 mA⋅h)
Bottom: AAA battery (1000 mA⋅h)

General information
Unit systemNon-SI metric unit
Unit ofElectric charge
SymbolA⋅h, A h
Conversions
1 A⋅h in ...... is equal to tướng ...
SI units   3600 C

An ampere-hour or amp-hour (symbol: A⋅h or A h; often simplified as Ah) is a unit of electric charge, having dimensions of electric current multiplied by time, equal to tướng the charge transferred by a steady current of one ampere flowing for one hour, or 3,600 coulombs.

The commonly seen milliampere-hour (symbol: mA⋅h, mA h, often simplified as mAh) is one-thousandth of an ampere-hour (3.6 coulombs).

## Use

The ampere-hour is frequently used in measurements of electrochemical systems such as electroplating and for battery capacity where the commonly known nominal voltage is dropped.

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A milliampere second (mA⋅s) is a unit of measurement used in X-ray imaging, diagnostic imaging, and radiation therapy. It is equivalent to tướng a millicoulomb. This quantity is proportional to tướng the total X-ray energy produced by a given X-ray tube operated at a particular voltage. The same total dose can be delivered in different time periods depending on the X-ray tube current.

To help express energy, computation over charge values in ampere-hour requires precise data of voltage: in a battery system, for example, accurate calculation of the energy delivered requires integration of the power delivered (product of instantaneous voltage and instantaneous current) over the discharge interval. Generally, the battery voltage varies during discharge; an average value or nominal value may be used to tướng approximate the integration of power.

When comparing the energy capacities of battery-based products that might have different internal cell chemistries or cell configurations, a simple ampere-hour rating is often insufficient. For example, at 3.2 V for a LiFePO4 battery cell, the perceived energy capacity of a small UPS product that has multiple DC outputs at different voltages but is simply listed with a single ampere-hour rating, e.g., 8800 mAh, would be exaggerated by a factor of 3.75 compared to tướng that of a sealed 12-volt lead-acid battery where the ampere-hour rating, e.g., 7 Ah, is based on the total output voltage rather phàn nàn the internal cell voltage, so sánh the 12-volt output of the example UPS product can actually deliver only about a third of the energy of the example battery, not a quarter more energy. But a direct replacement product for the example battery, in the same size factor and comparable output voltage and energy capacity but based on LiFePO
4
, might also be specified as 7 Ah, here based on output voltage rather phàn nàn cell chemistry. For consumers without an engineering background, these difficulties would be avoided by a specification of the watt-hour rating instead (or additionally).[citation needed]

## In other units of electric charge

One ampere-hour is equal to tướng (up to tướng 4 significant figures):

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• 3,600 coulombs
• 2.247 × 1022 elementary charges
• 1.079 × 1013 statcoulombs (CGS-ESU equivalent)
• 360 abcoulombs (CGS-EMU equivalent)

## Examples

• An AA size dry cell has a capacity of about 2,000 to tướng 3,000 milliampere-hours.
• An average điện thoại thông minh battery usually has between 2,500 and 4,000 milliampere-hours of electric capacity.
• Automotive siêu xe batteries vary in capacity but a large automobile propelled by an internal combustion engine would have about a 50-ampere-hour battery capacity.
• Since one ampere-hour can produce 0.336 grams of aluminium from molten aluminium chloride, producing a ton of aluminium required transfer of at least 2.98 million ampere-hours.