Recievers are limited to a 3A output max. This is why on giant scales you see multiple recivers and others prefer only to run the signal wire to the reciver and have a seperate wiring harness for the power of their servos (my preference).
When you charge a 6V batt. pack, it will charge up over 7V easily. This is not good for your receiver. A high voltage input to the receiver will shorten it life cycle (usually when you're real close to the ground ). I know of people that do not run a regulator, and I've seen that some of them have had problems. Personally, I won't run a 6V batt. pack without a regulator, though is just my opinion.
Kevin