340 watts is a about a 28 amp draw. Way to much for the Optima for any lenght of time. Batteries should be sized for a 5 hour discharge to 80% DOD, (depth of discharge), minumum. The Optima is rated at ~ 55 A/H to 100% DOD. You really need 3 to do the job. 2 will do for short time periods. 

Dennis

----- Original Message -----
From: Brian McCartney <monoscope@GMAIL.COM>
Date: Monday, July 24, 2006 1:14 pm
Subject: Re: Trickle Charger (follow up 182 Amps)

> I'm curious if you had problems with the Surepower isolator�
> �I've got one and an optima that's always been a little bit of a pain
> in the ass.
> The Surepower isolator was recommended to me by an electrical guy 
> as I
> run a pretty big amp (340w) off the spare battery.
> 
> 
> 
> On 7/24/06, Loren Busch <starwagen@gmail.com> wrote:
> >  RE: Aux Batteries
> > I've stayed out of the various recent battery threads because I 
> don't have
> > anything to contribute beyond what was being said.  But Dennis 
> just made a
> > good point that I want to second based on my experience over the 
> last 10+
> > years, first with an '85 Westy with a Surepower isolator and the 
> last four
> > plus years with a '90 Westy and the basic relay setup.  I've 
> only used a
> > stock Group 41 lead acid starting battery for the aux battery 
> from day one.
> > Simple reasons:  ease of install and cheap.  I went through 2 
> 1/2 batteries
> > in ten years in the '85, one so far (replaced the battery that 
> came with) on
> > the '90.  For the price of a Group 41 at Costco (no longer 
> carrried in my
> > local store) or at Wallyworld I can go through three or four 
> batteries> before I meet the cost of an Optima yellow top and 
> don't have the hassle of
> > mounting the Optima.  I play the stereo a couple of hours a day, 
> run a
> > laptop an hour a day or so (process pictures and watching the 
> news on TV)
> > and have gone to all LED bulbs internally (stock lighting plus 
> three other
> > lights I've added).  I just came in last night from six days and 
> nights> parked without starting the Westy and when I packed up to 
> leave there was
> > still plenty of juice left in the aux battery when I checked the 
> meter I've
> > installed just to see.
> > So if you are a little miserly with the electric usage the 
> cheapest and
> > easiest way to go is the stock Group 41 starter battery under 
> the drivers
> > seat.  KISS
> >
> > Footnote:  If I were fulltimeing or doing a lot of extended 
> camping I'd pick
> > up a little Honda generator, fill my spare gas can, fire up, 
> plug in, sit
> > back and relax.
> >
>