my black&decker booster pack(rated at 300 amps instantaneous) has a lead-acid 9AH battery in it... at a full charge, i've managed to turn over and fire a ford 4.6 with a VERY weak battery with it before, no intentional waiting with it hooked up to try and transfer as much current as possible before cranking.
with a 6AH unit..... i would certainly give it as much time as reasonable before attempting to crank to make sure that it could be done in a single cranking attempt, since i don't know how many other chances one would get with that capacity.
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