John,

I believe your failure analysis is flawed. Plugging the two battery packs in separately instead of through a single Y-harness, does not help against a pack failing by short. The bad pack will still pull down the voltage and power of the second pack. There is very little difference (in electric circuit terms) in either arrangement. To avoid problems due to a pack failing, we are better off using 5 cell packs and voltage regulators. This is the best way I know of to isolate the packs.

Plugging both packs through their own switch harness into a single Y-harness will give you switch harness redundancy.

Bedford