Dual battery with twins...
 

OK Gang, quick question...I have a late 29 Fever with twin SB's. The question is how do most of you run your battery switching while underway? I believe that most Fountain twins have two batteries and two switches. I think I read a service bulletin from Mercury Marine that recommended running the batteries to their respective engine i.e. #1 battery/#1 engine - #2 battery/#2 engine and NOT run the switches in the ALL position. The reason for this was to ensure the ECU had the proper voltage at all times when underway. I have heard that running in the ALL position never allows the batteries to be completely charged. I am far from an electrical engineer and would like to have any input as to what others are doing with regard to battery "switchology". Like to hear from all interested parties. One more day to spring!

GF

I got twins, 2 switches, 2 batteries also and for the life of me I can't figure out how these damn things are wired up and which does what. So I just run with both switches in 'both' all the time. So far ok.

I take the Single Point of Failure approach: if you have both switches set to "all", then effectively you have just one battery, with double the amperage. While running, anchored, whatever, and something drains your "single battery" you're done.

Two batteries give you redundancy, provided they are operating independently. Switch engine 1 to the "1" setting, engine 2 to the "2" setting, and you're protected from battery drain.

Say battery "1" dies. You can switch number "1" switch to "2" position, and get the number "1" motor fired up, then switch back to "1" position to attempt to charge the dead battery. If there are electrical problems that won't let the motor run or won't charge the dead battery, then switch the number "1" switch back to the "2" position and be happy that you're on your way home.

Brian, US1,

Thanks for the input, I believe that most people use the both or all position as does US1 but the fail-safe method that Brian suggests seems to be the right way to do it. I need to research that Mercury service bulletin and post it for more clarification, they were very specific about battery switch position. I also agree with US1 about trying to figure out which battery is which, I guess I will have to use trial and error to work that one out. Thanks again.

G-

Dang it guys, now I got to go out with a note pad and spend a couple of hrs and figure this out. I do know that one of the batteries seems to operate some of the acc. while the other operates some other stuff. Just never did see any type of method. I do switch 1 battery off when we over nite on the lake, but turn it back to both in the morning.

I will use p4-33 advice. Thanks

The Merc service bulletin is saying the same thing I am, run each motor off it's own battery. They're just telling you this for different reasons - to keep power constant to the ECU.

Powering them separately is a good practice whether you have EFI or carb motors, or even outboards. The idea is, if you're using "all" and your battery goes dead, they're "all" dead.

US1, my boat also runs some accessories off of one battery, and some from the other. I think they do this to avoid killing one battery all of the time. On an overnighter, just shut off the one you don't need. That way you're sure to have juice in the morning.

Gettin' warm out... won't be long!

See you guys.

my 35 has 4 batteries how do i run it haven all

4 battery switches, too? You need to know which switches go to which batteries. Switch two switches to 1, other two to 2.

If only two switches, then you probably have two batteries wired in parallel, and one switch controlling the pair. Treat these like one battery, and run one motor from it. Run the other motor from the other pair.

Of course, this is only a guess, as I've never used such a setup.

I have seen many boats set up with three batteries, one dedicated to running accessories and the other two held in reserve for starts. Three can get a bit confusing especially when they are routed thru a shorepower distribution box...way beyond my limited talents. I don't believe I have ever seen a 4 battery setup, I agree with Brian that odds favor two batteries are connected in parallel and treated as one unit per switch, yes??

G-

4 Batteries??????????
 

Man that is a bunch of excess weight in the rear of the boat! If that were mine I would carry a small booster/jumper, get rid of the two extra batteries and add a small gel cell to power the stereo and other accessories.