[BrianG]

I personally wouldn't use the 2nd diagram.

First, the ESC's BEC can power the receiver by itself with ease. Also, putting the receiver on a different BEC circuit than the servos might provide cleaner power to the receiver (and less chance of odd "reboots" if using Spektrum).

Second, there is really no benefit to using a separate battery for the BEC. It's just one more thing to charge and more weight. Any gains in runtime using a seperate battery for the BEC would be canceled out by the weight of that battery. If you really want to put the servos on their own battery, just get a 2s LiFe pack and hook it directly to the servos without a BEC at all.