Jim,

You're right, it's not a switch. (The switch is separate and connects to the power distribution unit, DPSI RV).
The BMS is just used to monitor and record battery use.

I had to order the BMS from [link=http://www.rc-electronic.com/html/englisch/englisch.html]Emcotec[/link] in Germany.
Desert Aircraft USA carries Emcotec products but they were out of this piece. They also make a single version of this unit if using one battery.