I have a Guest battery switch and 2 Optima D34M batteries.

My previous boats only had one battery. What is the best strategy for keeping my batteries in good shape?

Should I run with the switch on "both", or a single battery? Usually the only accessories I run is the stereo for short periods of time, NO amps, subs, etc.

I always run with the battery on either number one or number two. Never on both.

i usualy use no1 battery one day and no2 battery the next day and so on.

Keep the switch on just 1 battery. Install a battery relay/combiner between both batteries, approx $75 from Blue Seas. That will keep both batteries fully charged, yet will never drain both. Keeps 1 battery fully charged incase you run the other dead for some reason. No messing with battery switches needed, unless you do run 1 dead, then just switch to the good battery to start.

The relay does the same thing as running on both while the motor is running, then disconnects the 2 when you stop. All automatically.

Thanks Guys!

Is this what you are talking about? http://bluesea.com/category/2/productline/overview/387

You already have the switch, so I wouldn't waste your time running a combiner or isolator. Just alternate which battery you run off of to keep them healthy. I don't like run off the both position for extended periods. Its harder on the alternator.

I tell my customers to run half of the day on 1 battery, then go to the other for the second part of the day. No need for an isolator since you already have the switch and only one alternator.
Eddie

The combiner does the switching for you. If you don't mind remembering to switch it, then no, not needed. But you want it done for you w/o ever having to think/remember it, can't beat it. 1 relay, 2 short battery cables, 1 ground wire and 5 minutes to install.

Yes, that's the one.