You are correct but as a practical matter this is not a real worry if the owner
is paying attention. If the primary battery was shorted, the van would have
starting problems. If the auxiliary battery was shorted, the led panel would show
the failure when the engine was not running. There is a way to avoid the various
drawbacks to different aux bat systems but these cost money. Any real boat supply
store has or can get devices that sense the charge of each battery and direct the
charging current as needed while preventing each from draining back into the
other. Someone should investigate this and report as to the suitability for a
Westy installation. I will not be that person.

Mark

L&A Johnson wrote:

> This configuration fails if one of your batteries is bad (shorted internally,
> the usual death of old batteries). In this case the dead (bad) battery takes
> most of the charge current to the detriment of the other (good) battery.
>
> BTDT
> Larry