ATTN: Suriano
This post is for all, of course, but Suriano and I have discussed how to do this before.
I came across this excellent primer on battery wiring and charging over at helifreak:
Lipo Pack WiringThis is a great HTML page with interactive diagrams and calculators, including info on how to build a wiring harness to charge two packs at once when you have them connected in series.
Very Cool;
Mick