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Is it possible to measure the capacity of a battery if the discharge curve of the battery utilizes a resistor as the load? For example, if a 100 ohm resistor is connected to a battery and then the battery is discharged, would it be possible to calculate the capacity of the battery, based on this curve with this particular resistor (as the load)?

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In terms of energy I'd say kind of yes. Let's say you have the 100 ohm resistor, you can take the voltage reading every minute or so. Then, you can record this over time for the duration of discharge. Now, since resistance is constant, by using Power = V^2/R, you can get power at that moment and graph the power over time or just get the voltage graph and divide the whole ting by resistance. Since energy is power integrated over time, you can take the area of the curve you drew and you can say that's the energy that came out of the battery. Though, to get the actual energy, there's things like ESR and other factors but it should be a decent estimate.

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    \$\begingroup\$ Oh, and another thing, you don't want to do this for every battery especially rechargeable batteries. If it's like a duracell throwaway go ahead, but if it's something like a lithium ion batteries, fully draining the battery can seriously damage the batteries cycle life. \$\endgroup\$ – FressenUndFurzen Aug 3 '15 at 22:53
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    \$\begingroup\$ I disagree. Hence in our replies to @user5139637 we have advocated a constant current load. Unless your purpose is for your battery to power a constant resistance load, eg a simple torchlight. The results will not be meaningful to anyone wishing to use your battery with a boost converter for example. Until you work out what your battery is to be used for you are wasting our time. \$\endgroup\$ – BenG Aug 3 '15 at 22:54

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