In looking at the UK publication "Volkswagen Camper"

There is a battery that is what appears to be two 12V batteries in one.
The battery has:"The Twinpower� Battery system has two 12 volt batteries
in one container with a microprocessorbased electronic controller. The
two batteries act in unison."

http://www.twinpower.com/

Does anyone have experience with this?

This does bring up the idea of having, in effect 4 batteries in a two
battery Vanagon.

Todd
'88 Westy