For my Cap I'm using a similar setup to Cambo. Parallel Hydrimax 2000mAH NiMH packs on 6V for the RX. Each pack has it's own MPI HD switch so failure of a switch should not be an immediate issue. A Hobbico Voltwatch under the canopy monitors the RX bus. Before flight, I can turn on each battery individually to check voltage, which includes the load of the RX and servos. A second Voltwatch monitors the 4.8V 1450mAH NiMH ignition battery, which has it's own MPI switch in series with an RCATs relay for remote kill. This is really nice because I know immediately if the kill switch happens to be off at the TX before I start flipping the BCMA 40 gas engine. If I have two green LEDs from the Voltwatches, we're good to go. This system has worked great so far, is simple, and inexpensive for the redundancy offered.

If I were starting over, I would look hard at the A123 batteries. They are Lithium-Iron chemistry, I think, developed by DeWalt for power tools. There is a good thread in the Gas Engines Forum that will tell you most of what you need to know. Looks like the A123s are going to be the most bang for the buck with few of the issues that LiPos have. You can get by without regulators for the most part, and they have great capacity and fast recharge times. Aerobob is using a single A123 pack to power both his ignition and RX, or at least he was when I last checked that thread.