I skip the regulator and use A123 or Life batteries. That gives 6.6vdc at 2300mah per battery. One battery should be fine for 3-4 10min flights on a 50cc plane, and they can be charged in a few minutes at the field. The high charge rate and safety is what sold me on the Life's. Also get more charge cycles. If you want the redundancy/weight, you can add more. Your call on that.