Thanks guys for the input, very much along the lines of how I was thinking.
Suggestions on switches for this set-up anyone? Ideally something with 18awg, or there abouts, input wire from the A123 and dual out leads to the rx. I prefer the idea of a failsafe switch rather than a mechanical one. This way I get the dual input to the rx and the commercial A123 packs are ok as I haven't found anyone that supplies with dual output leads yet.
Something along the lines of the SF reg with ping and flag which I have already would be great but without the reg. I can't find a product like that yet
Cheers