An ampere-hour or amp-hour (symbol: A⋅h or A h; often simplified as Ah) is a unit of

electric charge Electric charge (symbol ''q'', sometimes ''Q'') is a physical property of matter that causes it to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative''. Like charges repel each other and ...

, having dimensions of

electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...

multiplied by time, equal to the charge transferred by a steady current of one ampere flowing for one hour (3,600 seconds), thus equal to 3600 A⋅s or

Coulomb The coulomb (symbol: C) is the unit of electric charge in the International System of Units (SI). It is defined to be equal to the electric charge delivered by a 1 ampere current in 1 second, with the elementary charge ''e'' as a defining c ...

. 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 Electroplating, also known as electrochemical deposition or electrodeposition, is a process for producing a metal coating on a solid substrate through the redox, reduction of cations of that metal by means of a direct current, direct electric cur ...

and for battery capacity where the commonly known nominal

voltage Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...

is understood. A ''milliampere second'' (mA⋅s) is a unit of measurement used in X-ray imaging, diagnostic imaging, and

radiation therapy Radiation therapy or radiotherapy (RT, RTx, or XRT) is a therapy, treatment using ionizing radiation, generally provided as part of treatment of cancer, cancer therapy to either kill or control the growth of malignancy, malignant cell (biology), ...

. It is equivalent to a ''millicoulomb''. This quantity is proportional to 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 Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

, 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 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.

In other units of electric charge

One ampere-hour is equal to (up to 4 significant figures): * 3,600

coulomb The coulomb (symbol: C) is the unit of electric charge in the International System of Units (SI). It is defined to be equal to the electric charge delivered by a 1 ampere current in 1 second, with the elementary charge ''e'' as a defining c ...

s * 2.247 × 10²²

elementary charge The elementary charge, usually denoted by , is a fundamental physical constant, defined as the electric charge carried by a single proton (+1 ''e'') or, equivalently, the magnitude of the negative electric charge carried by a single electron, ...

s * 0.03731 faradays * 1.079 × 10¹³ statcoulombs ( CGS-ESU equivalent) * 360 abcoulombs ( CGS-EMU equivalent)

Examples

*An AA size

dry cell An electric battery is a source of electric power consisting of one or more electrochemical cells with external connections for powering electrical devices. When a battery is supplying power, its positive terminal is the cathode and its nega ...

has a capacity of about 2,000 to 3,000 milliampere-hours. *An average smartphone battery usually has between 2,500 and 6,000 milliampere-hours of rechargeable electric capacity. *Automotive car starter batteries vary in capacity but a large automobile propelled by an internal combustion gasoline engine would have about a 50-ampere-hour 12 V battery capacity. * Battery electric vehicle capacities are usually given in kWh, but in 2013, the BMW i3 60 Ah was named after the capacity of one of its 96 cells, for a total of 96x3.6Vx60Ah=20,736Wh with about 18 kWh usable energy, to match the number of the entry level Tesla Model S60 which had 60 kWh. Later BMW i3 had 94 Ah and 120 Ah batteries, each topping Tesla's S85, S90 and S100 designations. *Since one ampere-hour can produce 0.336 grams of aluminium from molten aluminium chloride, producing a kg of aluminium required transfer of at least 2980 ampere-hours.T. L. Brown, H. E. Lemay Jr, "Chemistry the Central Science", Prentice-Hall, 1977 page 562 One kilogram of aluminium commonly requires 15.37 kWh, thus electric power represents about 20 to 40% of the cost of producing aluminium.

References

{{Reflist Units of electrical charge Non-SI metric units

Use

In other units of electric charge

Examples

See also

References