ampere-hour

An ampere-hour or amp-hour (symbol Ah , A·h, A h) is a unit of electric charge, with sub-units milliampere-hour (mAh) and milliampere second (mAs). One ampere-hour is equal to 3,600 coulombs (ampere-seconds), the electric charge transferred by a steady current of one ampere for one hour.^[1]

The ampere-hour is frequently used in measurements of electrochemical systems such as electroplating and electrical batteries.

The commonly seen milliampere-hour (mAh or mA·h) is one-thousandth of an ampere-hour (i.e., 3.6 coulombs), and is a technical term for how much electrical charge a particular battery will hold. Small batteries, such as those in laptops and digital cameras, are often rated in milliampere-hours. As an example, digital camera batteries with higher mAh values theoretically last longer without requiring a recharge, allowing one to take more photographs before having to replace the batteries.

A milliampere second (mAs or mA·s) is a unit of measure used in X-ray 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 and is approximately equal to 26.8 ampere-hours, and is used in electrochemical calculations.

It is recommended when placing batteries in a digital camera that their mAh values match. Otherwise, it is possible that one lesser mAh battery will drain before the others, causing extra strain on the remaining batteries or causing the digital camera to not work until all batteries are replaced.

References

External links

• Batteries - a glossary of common terms.