The battery will take the amount of time dictated by the mAh charge rating of your charger and the battery mAh capacity, so if you have a standard Heng Long mains charger with a charge rate of 200mAh then you can work out that a 3400 mAh battery will take at least 18 hours to charge (anyone feel free to correct me if I'm wrong).

Make sure that the battery matches the charger type, you should not charge a Ni-mh battery with a Ni-Cad charger. Original Heng-Long battery and charger is Ni-Cad (or mine is anyway).