There's your answer. If you plan to fly more than 3 or 4 times a day, you either have to buy a quick peak field charger or plug your wallwart into your receiver pack for 4 hours between every flight.

A wall wart charges at 1/10th C for standard receiver packs (approximately 50 mAmps), whereas most peak chargers can be set to 1 C or do it automatically.
Dennis-