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Old 03-11-2014, 10:35 PM   #4
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You can look up the "amp-hour" rating for the battery in that jump starter pack.

Multiply by 12 (volts) and you get the estimated watt-hr capacity.

Divide by 2. Save this number

Take each you plan to charge and multiply nominal voltage by mah capacity. Divide by 1000.
That will be watt-hr capacity of the pack.

Divide the number saved above (1/2 watt-hr of the source) by the watt-hr of the battery to be charged. You now have the number of recharges you can expect. (without damaging the source battery)
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