Need advice on Battery Setup for Merc 470

[sevillity]

I want to improve my battery system for shear peace of mind... I curently have one lonely car battery rated for 500cca to start my 86 mercruiser 470. This makes me very nervous, only having one battery. Especially since I am installing a new stereo system, nothing fancy or amplified, but still...we will likley be floating around with the engine off listenting to tunes, and I do NOT want to be dead in the water for losing track of time and letting the battery discharge too much. So...

I wish to have a dual battery setup... is this okay with the factory charging system or should I wait until next spring when I do the much promoted alternator conversion?

When I do complete the dual battery setup do I...

have one marine starting battery + one deep cycle marine battery with a battery switch?
have two marine starting batteries with a battery switch?
have two deep cycle marine batteries with a battery switch?

Also, if I should be using one (or two) starting batteries, what kind of CCA should I be looking for? 500 seems like very little for this engine. If instead I should be using the deep cycle sort, what size?

In addition, is there any particular way a dual battery system should be hooked up/or used to provide optimum performance/longevity/peace of mind?

Thank you very much for your help! I am totally out of my element with charging systems/electronics/etc! Any help is MUCH appreciated!

 

[fmalott]

Re: Need advice on Battery Setup for Merc 470

electronics are my weak point also but i know a few people that have a starting battery for the boat and a second battery for the bilige pump and so if the boat fills up when turned off it will not wear out the starting battery so i think having a second battery for the bilige the radio should be alright i have a small atv battery for my biligepump

 

[Scott Farley]

Re: Need advice on Battery Setup for Merc 470

I just bought a dual purpose marine battery from auto zone for about $80 that I am using for extra power. I too was worried about drain with my newly installed stereo, gps, lights etc. If you are strapped for cash, you can run both without a switch by just hooking up your second battery in parallel with your original. Make SURE you do not hook them up series! You will toast everything electrical! An isolator (about 30bucks at most places) will charge both batteries but only discharge one to the engine. That way if you ran the stereo and lights enough to discharge one, your crank battery is still fully charged. If I remember right, the battery I bought at auto zone is about 700cca. I have mine just hooked up in parallel. Then, I left my stereo on all night just for a test, and in the morning the engine started right up! I recommend however, the isolator or dual switch. I ran an eight gauge positive and negative wire to the glove box area with a negative terminal strip for grounds and a fuse block for the stereo, a cigarette lighter for my million candelpower spotlight, and the aux. interior lights I put in. Good luck!

 

[thumpar]

Re: Need advice on Battery Setup for Merc 470

Here is what I did. I installed a battery isolator. Battery 1 is a normal starting battery that only runs the guages, trim and starter. Battery 2 is a dual purpose battery that runs everything else, stereo, lights, fish finder, trolling motor, ect. It was a very simple hookup. The nice thing about an isolator is that I can run the stereo until it drains the battery down and the starting battery is not effected.

 

[sevillity]

Re: Need advice on Battery Setup for Merc 470

Here is what I did. I installed a battery isolator. Battery 1 is a normal starting battery that only runs the guages, trim and starter. Battery 2 is a dual purpose battery that runs everything else, stereo, lights, fish finder, trolling motor, ect. It was a very simple hookup. The nice thing about an isolator is that I can run the stereo until it drains the battery down and the starting battery is not effected.

This sounds like a great setup. I am curious though how all these systems are wired to the dual purpose battery. Did you just run wires to a gang switch or something, and from there to your various accessories? Also how is the wiring done so that the second battery recieves a charge from the motor but does not supply the motor with a charge as well? The biggest concern I have thus far, is whether or not my charging system can support two batteries prior to the alternator conversion. Does anyone have a wiring diagram that shows something similar to what thumpar did on his?

 

[thumpar]

Re: Need advice on Battery Setup for Merc 470

The way I did it was to just take the wire from the alternator that normally goes to the starter (that is the charge line) and run it to the alternator spot on the isolator. Then run battery 1 to battery 1 on the isolator and battery 2 to 2. I then ran a separate wire from the second battery to the fuse panel up front. I used a surepower 702 but I have a regular 3 wire alternator. The reason the second battery can charge but not drain the first battery is the isolator. It is a big diode. The power can only go one way through.

Here is a PDF with different types of isolator installs. http://order.waytekwire.com/INC/Marine Bat Iso 180119A.pdf figure 1 is how mine is setup. Just remember that this is with 3 wire alternators and I don't know if it will work with the standard 470 charging. The tech guy at surepower was very helpful to me when hooking up mine. You might try contacting them.

 

[sevillity]

Re: Need advice on Battery Setup for Merc 470

Thank you for all your input!!! After doing much research, I think I'm gonna go with a simple battery switch, such as the Pelko dual battery switch, and try to mount it conveniently closer to the console rather than in the battery hold. That way, I will always have a reserve battery on deck with nothing drawing on it. I guess the idea is to charge both while boating, then while floating around switch it to one or the other, then back to both when boating again. Makes sense! The only remaining question I have is what combination of batteries should I run? A starter and deep cycle, two starters, two deep cycles, two combos? I guess it probably doesn't matter, and I am making too much of this... probably two combos is a safe bet but is bigger always better or should I buy a specific size?

 

[thumpar]

Re: Need advice on Battery Setup for Merc 470

Just make sure if you do mount the switch up front you use some seriously large wire. I used 4 gauge in my setup which is only a couple feet each. If you are going to run the starter through it I suggest 2 or bigger unless it is over 15 feet and would go with 0 or bigger.