Hooking up dual batts with out a selector swtich? 3.7 Mercrusier

[Newbie@boats]

Right now I have a single battery set up and I would like to throw in another battery, so I can listen to the radio and not have to worry about killing the battery to get the boat started.....

Heres my question...Will I hurt my charging system if I run 2 batterys?

If I were to hook 2 batteries would I just do + to + with a cable and - to - with another cable?

Any info is great, thanks guys!

 

[Eric 3.7LX Alpha 1]

Re: Hooking up dual batts with out a selector swtich? 3.7 Mercrusier

That would work, but in my opinion, it's better to have the switch so you can isolate the batteries when running accessories, and use one for starting, or switch to both if needed. Plus the switch makes it easier to work on the boat if you have to disconnect the battery, just switch them off.

Look at the attached diagram, both batteries (+) are connected together when switched to "all" at the "com" terminal

The way I have mine, all accessories on the boat, including power to the starter run off the "com" terminal. If I stop the engine, I switch to either batt 1 or batt2, which ever would be my deep cell, to run the accessories. When I want to start can try on that same battery, or switch to the other one which has been left alone, or both.

 

[Don S]

Re: Hooking up dual batts with out a selector swtich? 3.7 Mercrusier

It won't hurt the charging system, batteries would be hooked in parallel. (+ to +) (- to -).

 

[MarkSee]

Re: Hooking up dual batts with out a selector swtich? 3.7 Mercrusier

That would work, but in my opinion, it's better to have the switch so you can isolate the batteries when running accessories, and use one for starting, or switch to both if needed. Plus the switch makes it easier to work on the boat if you have to disconnect the battery, just switch them off.

Look at the attached diagram, both batteries (+) are connected together when switched to "all" at the "com" terminal

+1 for the battery switch as you said: "not have to worry about killing the battery to get the boat started."

To get that, you either want:
option 1: a battery switch so the battery (cabled to position #1) running the radio doesn't drain the starting (cabled to position #2) battery.
option 2: a battery isolator so a dead battery does not drain the good battery then you'll end up with what you're trying to avoid.

Mark

 

[Silvertip]

Re: Hooking up dual batts with out a selector swtich? 3.7 Mercrusier

Go out to your car and turn the radio on. Go back out the next day and see if your car will start. If it doesn't you have a bad battery and it is not due to the radio being on. A good battery will power a standard radio for many hours before it would fail to start the engine. People are way to paranoid and read way too much into dual battery systems. Most folks have no need for them. Certainly OK to add but if you can see shore from anywhere on the bodies of water you boat on, dual batteries are unnecessary unless you have a very high power audio system or some other high current draw accessory. Use the SEARCH feature on this forum using DUAL BATTERIES or DUAL BATTERY SETUP and you will have enough reading to make your eyes bleed.

 

[Jlawsen]

Re: Hooking up dual batts with out a selector swtich? 3.7 Mercrusier

The trick to running batteries in parallel is haveing two batteries that are identical and of the same age. If you're plans are to keep your starting battery fresh and you don't want to mess with a switch and an ACR then you'll need to charge the house battery separately and you can't run them in parallel.

The reason you shouldn't run them in parallel is because that's only extending your run time and not protecting your starting battery. The weakest battery in the pair will be the one that determines your max run time. If you're going to do it, get two new identical batteries and put a digital voltmeter somewhere and when it say's 11.9v you're done.

It's cheaper in the long run to just get a Blue Sea Add a Battery system with the ACR and never worry about it.

 

[Newbie@boats]

Re: Hooking up dual batts with out a selector swtich? 3.7 Mercrusier

Hmmm...I know on my 03 Chevy duramax I can leave the radio on over night and my truck will start up in the morning.

I got the second battery in there today, I'm not hooking it up to my main battery, until the boat is running.

Then when I stop I'll disconnect it and listen to my radio all day, and if the battery is bad or dead, I'll have a good charged battery in the boat at all times.

 

[NYBo]

Re: Hooking up dual batts with out a selector swtich? 3.7 Mercrusier

I hope you're planning on installing a switch. Futzing around with battery leads on a rocking boat can be major not-fun.

A dead battery in a land vehicle is almost always just an inconvenience. A dead battery in a boat can often have much more serious consequences.

 

[Jerryh3]

Re: Hooking up dual batts with out a selector swtich? 3.7 Mercrusier

http://www.charlesindustries.com/main/battcom.html

 

[Newbie@boats]

Re: Hooking up dual batts with out a selector swtich? 3.7 Mercrusier

^ that looks very interesting.

Can you explain a little further on how that works? And how would I install that?

 

[Silvertip]

Re: Hooking up dual batts with out a selector swtich? 3.7 Mercrusier

The data sheet explains how it operates and what it does. You install it like the diagram shows. Start the engine and both batteries are connected in parallel. Stop the engine the batteries are disconnected from each other.

 

[Newbie@boats]

Re: Hooking up dual batts with out a selector swtich? 3.7 Mercrusier

So I would just hook up my main starter/power wire to one terminal and all the other wires for the radio gps and what not to the other terminal?

 

[Silvertip]

Re: Hooking up dual batts with out a selector swtich? 3.7 Mercrusier

We have no idea how your boat is currently wired. IF -- note I said IF, all of your accessories are fed from a fuse panel you would NOT disconnect those and connect them individually to the isolator. You simply disconnect the postive feed to the fuse panel and connect it to the isolator. The positive terminal of the house battery also gets connected to the same terminal. You DO NOT change the wiring for the starting battery. You merely run a wire from the POS post of the starting battery to the applicable post on the isolator. You connect the NEG post on each battery together and go boating. I suggest you study that diagram closely. It clearly shows how this device gets connected.

 

[Newbie@boats]

Re: Hooking up dual batts with out a selector swtich? 3.7 Mercrusier

Well, I got both batteries in an hooked up, the boat starts up far more noticeably quicker then it did before and the voltage gauge is reading higher then it was before...only by about .5v I let the boat sit with the radio on...for a few hours and it started right back up.

I will be looking into that battery switch ASAP.