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Estimate Current Draw from a Battery

Find the current a load pulls so you can estimate battery runtime.

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Enter any two values and the other two are solved automatically

πŸ’‘ Ohm's law: V = I Γ— R. Power adds P = V Γ— I. Knowing any two lets you derive the rest β€” handy for sizing resistors, checking LED current, or working out heat dissipation.

Battery tips

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Enter battery voltage and the load resistance (or power) to get current draw in amps.

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Runtime β‰ˆ battery capacity (Ah) Γ· current draw (A) β€” lower current means longer life.

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Real batteries sag under load and aren't 100% efficient, so treat the runtime as an optimistic estimate.

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