RE: Power Expander or not -that's the question
Technically, sure, I guess you can say that a standard servo connector is "rated" at 3 amps continuous, for the sake of argument. But it can surge to double that or more for at least a second or two with little or no voltage loss. I charge my A123's through a standard lead at 3 amps and the lead doesn't even get warm.
I just did a hard, 12.5 minute flight with my 100cc Extra with 6 5955's and an 8711. Flight included a knife edge loop, fast-rolling loops and circles, blow-overs, tumbling maneuvers, etc. Pretty much stress-tested the plane.
I have an AR9000 standard 9-channel receiver, powered by two A123's through a wolverine switch with two standard leads going into the receiver. I then have a Fromeco DC-up plugged into the receiver. The DC-up has a low voltage recorder on it. Lowest voltage encountered was 5.9V. This was the second flight on the batteries' charge, so the voltage had already stabilized at 6.6ish.