ORIGINAL: Shogun
Jim,
If you use a single pack your system is drawing ALL of it's power through the two wire lead that comes off of that pack and delivers the power to the receiver bus. Adding a second pack adds another set of leads that feed the bus and thus each lead, from each pack respectively, only sees half the amp draw, reducing the possibility of a voltage sag. Of course this assumes the packs are of similar capacity and voltage.
Yes, I understand that the leads (or wires) coming from the batteries have their own limitations, and that by having two batteries you can double the amount of power going to the RX bus.
This has nothing to do with the amount of current that the RX bus can carry though. The RX bus still has it's limitations seperate from the battery leads. You can hook up 10 batteries to the RX bus if you want, but the RX bus is only going to pass so much current because it is only capable of passing so much current (Just like the battery lead can only pass so much current.).
This is the whole reason they've developed power distribution systems. In order to get enough power to the servos we need to bypass the RX bus and its limitations.
By using 2 batteries, you are getting rid of one weak point in the system, but the RX bus is another weak point.
One company I know of that has done some testing is Fromeco. Check out their website if you haven't:
http://www.fromeco.org/
Lots of good info on this subject there and lots of good products that solve the problem of limited capacity in our systems.
Jim