View Full Version : Need advice on changing dual battery setup

04-04-2011, 03:36 PM
I'm moving my batteries and battery switch and not sure the original setup was even right. Redoing it I want to make sure it is right this time.

I have a "hybrid" marine deep cycle starting battery (grp 29?) and a regular starting battery (grp 27). The diagram below shows the current wiring setup. The power lead for my amp distribution block was right off the same main lead that went back to my starter. The switch gives me the option to run Battery 1, 2, Both, or Off and for the last two years I've typically just left it in the Both position all the time.


USAGE: The stereo mostly is on while we're out running, sometimes while parked on the beach for an hour or so at a time. Three amps so it is pulling a fair amount of power. I've never had problems with battery drainage or not starting, even though my batteries are getting pretty old. I do stick them on a trickle charger when it is parked for a while.

So is it correct to run the amps from both batteries like the current setup or should I move it to just the deep cycle? I'm wondering if it could keep up by itself.

I don't really want to invest in a third battery which leads to my next question, could I just run two of the hybrid deep cycle starting batteries and keep the current wiring setup?

Also somewhat related, my amp grounds were going to the engine block on the same stud as the negative cable but I think that was causing a whine in the stereo. I'm going to move the amp grounds directly to the negative post on the battery. That seems like the "duh" thing to do?


04-04-2011, 09:34 PM
your new setup looks right to me...at least that is how mine is setup lol

04-04-2011, 10:05 PM
Seriously dude - is this right? It worked fine the way it was but I didn't sit with the engine off for hours cranking the stereo and runnning the battery(ies) down.

I know opinions vary some on how to set this up. I also don't to invest more into the controlled circuits that eliminate the need for a switch. It's not a big change, but I need to make a decision soon because once the cable is cut I don't want to be going back and splicing in to lengthen it after I change my mind....

And I sorta have doubts about one "stereo" battery handling three amps for very long with no juice coming from the alternator. (Kicker 750.1, Kicker 350.4 and Kicker 450.2)

04-04-2011, 10:22 PM
The starter/alternator cable, helm buss supply and amplifiers should all tap the common post of the dual battery switch. Nothing should go directly to the battery positives except for the '1' and '2' switch posts, a memory lead if you choose and a bilge pump/float switch when applicable. There's only one good way.
As a byproduct, one day when you change your batteries, if they are both deep cycle and symmetrical (usually fine in warm weather with a small block), you can alternate the battery functions with each outing and increase the longevity of your batteries.

Earmark Marine

04-05-2011, 01:04 AM
Thanks David. Exactly the type of answer I was looking for. So I basically have it setup the right way already (except for the amp ground which I will move). I can switch between batteries, charge both, etc.

Hey, nobody can question my intentions better than me...

04-05-2011, 04:03 PM
As a professional who's primary business is batteries, (we sell 12000 per yr currently) i have a bit of input and suggestion.

Your current suggestion of rewiring the switch is totally correct and changing the ground is also correct to prevent some interference, but because of the setup you will only minimize the noise. My personal opposition is that the switch be used as that ....a primary disconnect from the battery(ies) only. if you want to keep the current battery's you have i would change your setup slightly. the 2 battery's you have work TOTALLY different in the way they charge and discharge. because of this the battery are actually fighting each other and both battery will only work as good as the poorest battery.

The, well call it starting battery, is designed to have a quick charge and high amp output for starting periods and its not designed to be discharged past 75% "state of charge" which is about 12.4v approx. continual discharges beyond this warp the plates inside the battery and cause an effect called "treeing" as warping knocks off the plate material and it settles in the bottom and shorts the plates.

Oppositely, deep cycle battery's are designed to be discharged and recharged on a continual basis BUT not charged quickly as the charge is lost to surface charge and not a deep charge. because the plates are thicker and heaver they charge slower...its the nature of the beast. the hybrid is basically a deep cycle battery with the plates spaced apart with a sleeve to prevent warping and shorting.

I would highly recommend if you are going to keep the 2 different battery's that you use a battery isolator and split the system. the alt will charge both battery's anytime its running, but using the stereo or acc will all draw off the deep cycle only while sitting, leaving you a fresh starting battery so you always know you can get home. this will also not allow the battery's to "talk" to each other and both battery's will charge to there own capacity.

If you have any other questions feel free to ask away.

04-05-2011, 09:04 PM
So I've been searching for a good diagram on where the isolator would go with a dual battery and switch setup like I've sketched. Not really finding a "simple" answer.

The isolator goes between the batteries and the switch? Or does the isolator basically replace the switch?

Or is there an isolator with a switch built-in to it... Is that what the Blue Seas setup is I've heard so much about?


04-05-2011, 10:23 PM
A diode isolator may lose the better part of a volt. And, you really can't afford that. A lost volt could also represent 15 percent of your power on an unregulated amplifier and a fair percentage of your reserve time. I don't recommend them.
You're describing an ACR/VSR voltage sensing relay. The various schemes and schematics depend on the size of your system in both power and battery reserve capacity, whether or not the stereo is dependent on the helm electronics for control (like a screen) and how strict you want to be with your AC shore charging. If you don't mind the manual operation of a switch and you limit your batteries to the scenerio that you described then the switch will satisfy every need less the extra convenience of a "set it and forget it" ACR/VSR.

Earmark Marine

04-06-2011, 07:57 PM
David is right, there will be a voltage loss using an isolator, depending on the unit i have seen loss from .3 to .9 volt. seeing as alternators on average put out about 14.8 v and devices like amps and radios are usually designed to a voltage spec of 14.4v - your wire resistance......yes you would see a power output reduction of about 7-12% by my numbers. its not a lot....but yes a slight reduction in output, but i know i cant listen to my radio at max all day long. it becomes a personal decision.

the biggest problem you have is not how to wire this up....you have the right idea....honestly you need to ditch the "starting battery" and get second hybrid and go with a basic system through a switch. again the isolator solves a problem with your mismatched batteries but in term's of simplicity it can be a bugger if there are problems down the road.

04-06-2011, 08:04 PM
Berg - As a local guy you have a few beni's others dont on all this board. Hook up your boat. Drive it down to Lake Oswego Oregon, and we can show you what needs to be done face to face.

Our door is open to any boat, with any brand gear. We dont discriminate. Advice is free and its always fun to meet others in the local boating community.

Exile Audio

04-06-2011, 08:31 PM
Thanks again guys. I just took both batteries in for a full test and both are in really good shape for being older. Wanted to do that before the move so I'm not just pulling them out again in a short while.

I think for now, since I'm not really causing any harm, I'm going to run the setup as is until I need a new batt - then I'll get a more pro consultation and possibly swap in some new twins, etc.

Brian - My boat is still in a wintery cocoon for a while unfortunatley.