Regardless of what battery you have, you have to compare the mah (mili-amp rating) of the battery pack with what the charger will put out, and simply do the math.

For instance, if you have a 1000 mah battery pack and a 50 mah charger, then it will take 20 hours PLUS about a 20% overhead to take the battery from fully discharged to fully charged. If the battery is partly discharged, then it will take that much less time to re-charge.

CGr.