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Difference between revisions of "Battery capacity"
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Battery capacity is typically measured in milliamp-hours, or how many milliamps you can draw from a battery for how many hours? If you can draw 200 milliamps for 8 hours, then the capcity is 1600 mAh. The only way to actually measure the capacity is to do just that, drawing a known current and measuring the time until the battery is exhausted (or reaches some voltage that you set as the minimum). Some battery testers will try to measure the remaining capacity without discharging the battery, but this is not accurate. | |||
When comparing batteries of different voltages (for instance 1.2V NiMH vs. 3.6V li-ion), you have to determine the total energy of the cell. Power (P, measured in watts) is equal to electromotive force (V, measured in volts) times the current (I, measured in amps). So, for instance, a 60-watt lightbulb requires 60 watts of power to light up. But the power company bills you for watt-hours (converted to kilowatt-hours), because the total energy (E) they sold you is based on how many watts you were using for how long (t, time). For burning a 60-watt bulb for 24 hours, you would have to pay for 1440 watt-hours (or 1.440 kilowatt-hours). | |||
P = I * V | P = I * V | ||