>I was really referring to vehicles with an existing aux. gas heater.
>
>Also, I've got a mechanic replacing the (burnt out) aux. gas heater with
>another one he has.  When I asked him to wire the 12V to my second (Optima)
>battery, he went on and on about how it can't (translation: he doesn't want
>to - more work I guess) be done, and it has to go to the main starting
>battery.  "Why bother anyway, since running the aux. gas heater without the
>engine on would kill ANY battery very quickly anyway".
>
>Here's the big question:  How long can you run the aux. heater on battery
>only, before it kills it??

That depends on how much current it takes.
I'm remebering 4 amps myself (I put a bi-metalic household thermostat in
the westie so it didn't run all the time)

Your Optima will last about 12 hours at 4 amps. You should be running a
yellow top. Don't try this with a red top, you would kill it in short order
(50 cycles/RT vs 500 for a YT)

An Optima doesn't have a lot of reserve capacity, A group 29 marine battery
will last longer (almost 2X) but is also heavy and messy.

 -Otmar-
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