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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 ...
Capacity is usually stated in ampere-hours (A·h) (mAh for small batteries). The rated capacity of a battery is usually expressed as the product of 20 hours multiplied by the current that a new battery can consistently supply for 20 hours at 20 °C (68 °F), while remaining above a specified terminal voltage per cell.
Its capacity at 250 mA drain is 1,700 mAh at 1.5 V, less than other chemistries, limited by the low efficiency of the step-down converter. [21] Some later Li-ion AA batteries advertise their capacity in milliwatt-hours (mWh) instead of the usual milliampere-hours (mAh), so a customer's attention is drawn to the figure, typically a claimed 3,000 ...
For example, consider a battery with a capacity of 200 Ah at the C 20 rate (C 20 means the 20-hour rate – i.e. the rate that will fully discharge the battery in 20 hours – which in this case is 10 A). If this battery is discharged at 10 A, it will last 20 hours, giving the rated capacity of 200 Ah.
This results in a 500 mA USB device running for about 3.7 hours on a 2,500 mAh battery, not five hours. The Board of Trade unit (B.T.U.) [ 17 ] is an obsolete UK synonym for kilowatt-hour. The term derives from the name of the Board of Trade which regulated the electricity industry until 1942 when the Ministry of Power took over. [ 18 ]
The watt, kilogram, joule, and the second are part of the International System of Units (SI). The hour is not, though it is accepted for use with the SI.Since a watt equals one joule per second and because one hour equals 3600 seconds, one watt-hour per kilogram can be expressed in SI units as 3600 joules per kilogram.
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For example, an "overnight" charge, might consist of supplying a current equal to one tenth the ampere-hour rating (C/10) for 14–16 hours; that is, a 100 mAh battery takes 10 mA for 14 hours, for a total of 140 mAh to charge at this rate.