Adding 2nd battery in boat... have questions

I have an 89 baja sunsport 186 with Merc. 4.3L and Alpha One. I have one battery and the original 55amp alt which was recently rebuilt for me. I want to add a 2nd battery to run the radio off of and have a Solenoid swith. My question is, the solenoid I have been told to buy which I did has 4 connections on it. One for positive to each battery and then a ground and another hot wire which only turns on when I turn the key on. I need a suggestion or two where to mount the wire that goes hot when I turn the key. And maybe even the ground. I am going to mount the solenoid in the hatch and have the 2nd battery right behind the original. Oh and any kind of battery suggestions would be great as well. Thanks!

Re: Adding 2nd battery in boat... have questions

What kind of solenoid is this? Is it marine rated for spark?

Re: Adding 2nd battery in boat... have questions

I got it from the armature place I got the alternator rebuilt with a marine regulator. THey are really good, been to them before. He said that the solenoid would be fine. I dont think it is a marine solenoid, however, they do tons of work with Travis Boating Center and other boat centers around town.

Re: Adding 2nd battery in boat... have questions

Provided the solenoid is marine rated you are correct, the large posts get connected to the battery positives. Ground should go to the battery since you're probably mounting this near it.

Grab a multimeter and check to see if your ignition switch has a wire that has 12v dc ONLY when the switch is on, (possibly purple, i couldn't find a mercruiser diagram colors can vary by engine manufacturer) This is where you could tie in for your solenoid.

As an alternative you could mount a switch on the dash and flip it to combine the two, it sounds like you're going for an automatic setup so this may not be desired.

Re: Adding 2nd battery in boat... have questions

Ive been told I could run the other wire to the pink/white wire going to the distributor as a 12v hot wire when key is on? Is that correct?? Im having trouble since all my accessores can be run when the key is off.

Re: Adding 2nd battery in boat... have questions

Wouldnt it be easier to buy the standard Guest Battery switch that has Bat1 /Bat2 /Both / Off on it....

as for the battery types, you should go with a Starting Battery for the primary starting, somthing measured in Cold Cranking Amps CCA. the hight the number the better... For the "house Battery" you should get a deep cycle, measured in Amp/hrs... again the higher the number the better.

Deep cycle can also server as part time starting batteries in a pinch, but the cranking battery is not designed to have long periods of draw on them so they are not ideal for "house batteries"

That suggestion is the ideal setup, however you can get combo batteries, gel batteries and glass mat batteries... all these have their pros and cons...

Re: Adding 2nd battery in boat... have questions

you'll probably need to pop in the mercruiser engine forum and ask the guys there as I'm not familiar with what wires are what color on them. They should be able to answer where you can hook up for switched power real fast.

A 1/2/OFF/Both switch will allow him to have two batteries but he has to remember to switch the switches.

If you want a install and forget the solenoid is a good solution, an isolator is another way to do it and there are even voltage sensing relays from people like blue-sea-systems that don't require it to be hooked into the ignition system.