Only need an isolator if the batteries are in parallel. The standard setup with 2 batts keeps them each isolated from each other unless you hold down the metal pushbutton at the helm which allows them to work in parallel temporarily to start the engine(s).

Parallel gives you same voltage (12V) but combines the crank amps from each battery.

You may notice a black plate above the 2 batt swiches if you have them on the lower helm of a sedan model. That plate is an expansion slot for another switch to accommodate a 3rd battery which you can hook in parallel.

-Karl

Are your switches just on and off or do they have a "both" position?

In any case if you only have 2 batts on the boat I would never run them in parallel all the time.
You will find 1 of the 2 batts does most of the house work and the other is more of a reserve batt.
This way you will never be screwed if you run a battery in the ground. You will still have 1 remaining to start your engines. And if you push the parallel button you will get what little is left of the dead batt plus the good batt to start the engines.

I'm assuming since the parallel button was removed the switches have the "both" capability to run the batts in parallel all the time. Again, its just my opinion to parallel a 2 batt system only temporarily for engine ignition.

If you have 3 batts you can run 2 of them in parallel with isolator all the time and still keep the 3rd separate as your starting reserve. And then you could hook up a pushbutton to parallel all 3 batteries to start the engines.


-Karl

Wayne,

You should connect the battery switches so that either battery can connect to either engine, or both. The way I did it is shown at www.geocities.com/dougmrose under 32 Marinette Wiring.

If you can't start an engine, swap batteries to the opposite engine and try again. Check the alternator and the battery. If this doesn't work, parallel the batteries to get start current and then fix!

Otherwise, you should only use "Both" when engines are running, if then. I would not use an isolator, I would use a combiner like http://store.hamiltonmar.../browse.cfm/4,6007.html . it is expensive, and when I have time I will make my own.

The only problem with combiners or isolators is that you can lose an alternator and never know it. If the systems are separate, it is pretty obvious pretty soon.

Eddy: I am among those who shut it off. My orig charger cooked the batteries. I think my updated unit (now 10+ yrs old) would probably not cook the batteries. But I'm still cautious so I try to run only when we visit the boat and don't run the engines much (we aren't doing much engine-running or visiting this crummy season).
One disadvantage to my method of operation: say, for some awful reason, the bilge pump needs to run a lot, the charger would supply much of the juice to keep it running for a longer time.
It'll be interesting to hear the chorus on this.

110 volt sump pumps,110 volt sump pumps, 110 volt sump pumps!!! If you are going to reley on Batts only, leave charger ON and install a hot water heater timer on battery charger to let it run an hour or so a day to keep from frying batts!! Sorrydog