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If battery is a voltage source then why current is mentioned ? The current depends on the resistance in the circuit right? Then how can a battery give mAh as well as voltage?

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    \$\begingroup\$ mAh isn't a unit of current. It's a unit of how much current you can draw continuously for an hour before the battery dies. \$\endgroup\$ – tangrs May 13 '15 at 1:08
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mAh is a measure of battery capacity, not instantaneous current. A 1000mAh battery can theoretically sustain a draw of 1000mA for one hour before it runs out. Broadly speaking, that means it could also sustain a draw of 500mA for two hours, or 2000mA for half an hour, but in reality battery capacity varies somewhat depending on how much current you draw; lead acid batteries, for instance, have significantly more capacity if discharged slowly.

The product of a battery's mAh rating and its voltage gives a rough approximation of power capacity (in watt hours) - rough, because a battery's voltage will also vary during the discharge cycle.

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