# Ampere-hour

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A 2500 mA·h AA and a 1000 mA·h AAA rechargeable battery

An ampere-hour or amp-hour (SI symbol A·h or A h; also denoted Ah) is a unit of electric charge, equal to the charge transferred by a steady current of one ampere flowing for one hour, or 3600 coulombs.[1]

The ampere-hour is frequently used in measurements of electrochemical systems such as electroplating and electrical batteries. The commonly seen milliampere-hour (mA·h or mAh) is one-thousandth of an ampere-hour (3.6 coulombs). Using a digital or analog voltage/amp meter, set the dial to the appropriate suspected mAh/dc setting, place probes on correct anode terminals, i.e. "+" for positive battery end, "-" for negative end. Positive (red), negative (black), if wired to battery or batteries. Read accordingly. If digital meter has 1 amp or larger setting, any reading under 1 mAh will show 0.75 or 750 mAh, as an example.

$\mathrm{A{\cdot}h}=(3600\,\mathrm{s})(\mathrm{A})=(3600\,\mathrm{s})(\mathrm{C} / \mathrm{s})=3600\,\mathrm{C}$

A milliampere-second (mA·s) is a unit of measure used in X-ray imaging diagnostic imaging and radiation therapy. This quantity is proportional to the total X-ray energy produced by a given X-ray tube operated at a particular voltage.[2] The same total dose can be delivered in different time periods depending on the X-ray tube current.

The Faraday constant is the charge on one mole of electrons, approximately equal to 26.8 ampere-hours. It is used in electrochemical calculations.

An ampere-hour is not a unit of energy. 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 approximate the integration of power.[3]

An AA size dry cell has a capacity of about 2 or 3 ampere-hours. Automotive car 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 aluminum from molten aluminum chloride, producing a ton of aluminum requires transfer of at least 2.98 million ampere-hours. [4]