You can look up the "amphour" rating for the battery in that jump starter pack.
Multiply by 12 (volts) and you get the estimated watthr 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 watthr capacity of the pack.
Divide the number saved above (1/2 watthr of the source) by the watthr of the battery to be charged. You now have the number of recharges you can expect. (without damaging the source battery)
