Battery combiner

[Sean]

Here you Chuck may not be a big deal after all www.texasindustrialelectric.com/relays_1119845.asp called a series parallel switch 

That's a great find, Clifford.  At $140 it is less than I would have thought.

This solenoid has the proper break-before-make, double-throw action that is required for the task.

Depending on the sizes of the banks being bridged, I would be concerned about the rating of the smaller terminals and the continuous rating of the flow-through (resting) path between the banks.  It looks to be sized basically for two single batteries.  If that's all you plan to use, it should do the job.

-Sean
http://OurOdyssey.BlogSpot.com