LiPo capacity: milliamp-hours, runtime and size
Capacity, in milliamp-hours, says how much charge a battery holds. This guide explains how to turn a runtime target into a capacity figure, and why the biggest capacity is not always the right choice.
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Runtime follows a simple relationship: a device drawing a steady current will run for roughly the capacity divided by the current, before efficiency and cut-off losses. A 1000 mAh battery feeding a device that draws 100 mA runs on the order of ten hours; the same battery feeding a 1000 mA load runs on the order of one hour. That arithmetic is approximate — real runtime depends on the discharge curve, the temperature and the device's cut-off voltage — but it is the right starting point for sizing.
Capacity costs size and weight. A 5000 mAh cell is physically larger than a 1000 mAh cell of the same design, and a device with a fixed cavity cannot simply take the largest capacity on offer. The selection sequence is therefore: fix the cavity, find the largest capacity that fits it at the right voltage, and check that the runtime meets the target. If it does not, the answer is usually a device redesign or a lower-power operating mode, not a request for a physically impossible cell.
Capacity figures on this site belong to individual listings. The representative 803040 listing states 1000 mAh for that listing; another 803040 listing states 450 mAh. Quoting a model number without its capacity invites the wrong cell, so every inquiry on this site should pair the two.