You can check out Cole Hearse. They make cut off switches in several confirurations.
I have not seen anyone run the dual 12/16 volt program. I know that in a blown deal we ran 12/24 volts with 2 12 volt batteries and thought it worked very well...The only item that ran on 24 volts was the starter. Everything else ran on 12 volt. Spun the motor over hard. Hot/cold never missed a beat. it was a 532. 11-1.. 1471 30% over