I have one of those RX's.

It is single conversion, and fairly short ranged. I have flown "up and out" with it when I was by myself, but I've also taken radio hits on it when other guys were flying. (it was a 2IM thing, I'm on channel 27, another TX on 50 will hit my RX).

Anyway, chance are, you're going to use the BEC connection from the flight battery as Time Pilot mentioned. In that case, just use the correct battery for your motor/airplane, the speed control will take care of the receiver power just fine.

If you are going to use a seperate receiver pack for some reason, I'd just go with a "normal" 4-cell pack. If you're using Nicads, that will be 4.8volts. If you have a dry cell pack (where you put in disposable batteries), then the pack will start at 6v (4 * 1.5v), and drop off. You'd change the batteries when they get to 4.8v

I also agree with Crashem, I don't think this RX is suited to anything other than small park fliers that will be kept fairly close in.