Ampere-hour

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 understood.

A milliampere second (mA⋅s) is a unit of measurement used in X-ray imaging, diagnostic imaging, and radiation therapy. 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.^[3] 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.^[4] Generally, the battery voltage varies during discharge; an average value or nominal value may be used to approximate the integration of power.^[5]

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 lithium iron phosphate battery cell (LiFePO
₄), 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 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 than the internal cell voltage, so 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 form 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 than 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]}

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

• 3,600 coulombs
• 2.247 × 10²² elementary charges
• 0.03731 faradays
• 1.079 × 10¹³ statcoulombs (CGS-ESU equivalent)
• 360 abcoulombs (CGS-EMU equivalent)

• An AA size dry cell has a capacity of about 2,000 to 3,000 milliampere-hours.
• An average smartphone battery usually has between 2,500 and 4,000 milliampere-hours of electric capacity.
• 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 aluminium from molten aluminium chloride, producing a ton of aluminium required transfer of at least 2.98 million ampere-hours.^[6]

• Electrochemical equivalent
• Kilowatt-hour (kW⋅h)