OK - I thought I had this figured out

[daboys]

I have dual batteries and a dual battery switch with a 1,2, both, off setting for each battery. I thought I should run one battery on 1, the other on 2 - I turn off both when the boat is not in use. I had the boat in for a checkup and when I got it back from the mechanic the battery switches were set to both - so now I am confused, is the mechanic correct and each battery switch set to both or should I continue to run one on 1 and the other on 2 or doesn't it matter either way - many thanks to the knowledable posters on the board.

[oldLenny]

I don't understand why you have "two" switches. In my way of thinking there should be only one controlling both batteries. You need to isolate, when running, one of these two as the alternator will not like the "reserve load" it sees and has to "put out" for. A diode in line will isolate this. I have always been under the impression (and used mine this way) that you run on one or the other. If you are anchored or tied up and drawing power all day long and not running, then I switch to the other one. When it is time to go I switch back to the main one to start if needed. Then you just select with one needs to be toppped up again. When you are in a pinch you can switch to "both" to bridge them in parrallel and in theory double your current if they were full to get you going again.

I wouldn't have them "both" selected in parrallel accepting a charge from the alternator if it were me. I have also seen the weaker battery in a parrallel charge set-up become DIS-charged when on both and the charge go to the other one equally as this one loses out.

There is a "dual battery" lay-out on this site under this "Performance talk" area.

http://www.donzi.net/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=004872#000004

...do you have one motor or two?,...what type boat?


This is a good question for Forrest as he is running three batts with twins in his Magnum.

[daboys]

Lenny,
I am running a 2001 28 ZXO with twin 5.7L. I think - but who am I to know, that by putting one battery on 1 and the other on 2 that I am using 1 battery as the primary for engine 1 and the other battery as a primary on engine 2. The radio and miscellaneous gear runs off battery 1 (I know this because when battery one is offf I can't turn the radio or cabin lights on)- are you confused yet???

[MOP]

Except for the auto bilge pump which should be directly fused and connected to the battery all other things should be wired to the common post of the switch so anything can be operated in either position. A nice thing to add is a battery islolator that will keep both batteries charged at all times no matter what position the battery switch is in.