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Old     (ramhouse)      Join Date: Apr 2004       04-03-2005, 9:54 PM Reply   
Looking to adding second battery after all these years. Know it's not that hard, but need direction and or diagram.
Old     (chevboy171)      Join Date: Feb 2005       04-04-2005, 1:54 AM Reply   
Positve to positive, negative to negative.

Run a cable from the positive of your existing battery to the positive of your new battery and a second cable from the negative of your existing battery to the negative of your new battery...this will keep the voltage the same (at 12 volts i assume)
Old     (wakeme884)      Join Date: Jul 2004       04-04-2005, 7:36 AM Reply   
heres a little more detail.....
Old     (jklein)      Join Date: May 2001       04-04-2005, 8:11 AM Reply   
see for more info... I'm certainly no expert.

I think it depends on what you want to do. There are two basic configurations from what I understand:

1. Accessory Battery
2. Alternate Battery

The Accessory battery is supposed to be used to run all the accessories (usually an audio system) and has an isolator run between the main battery and the accessory battery. When charging, both batteries charge. However, when running the accessories, the acessory battery is isolated from the main battery so the main battery will not discharge, leaving it fresh for cranking your engine. In summary both batteries are always isolated except when charging. The acessory battery would have to be disconnected and connected to the main battery leads if you had a dead main battery. This is what I'm running.

2. Alternate Battery. Both batteries charge as in the accessory battery case, but the alternate battery is isolated in the sense that if the main battery is dead, you can switch to the alternate battery for cranking. All accessories run off the main battery.

FYI: Some people run a thing called a perko switch that allows them to run an accessory battery, with a manual switch that can switch to the acessory batter if the main is dead.

see for more info... I'm certainly no expert.
Old     (mikeski)      Join Date: Aug 2003       04-04-2005, 10:13 AM Reply   

Looks like the X9 on that site has one of those 150amp alternators from batteryshack that is not ignition protected. Anybody looking through this thread you should not buy this alternator, it does not have the required safeguards to protect your boat from exploding if there are ever gas vapors present in your bilge. This was posted by Grant an others in previous discussions.
Old     (acurtis_ttu)      Join Date: May 2004       04-04-2005, 10:39 AM Reply   
FYI, Thru another guy on here found a 135 amp marine alt from a guy in dallas. $109, plus shipping. works very good the last 3 weekends. shows 14.1-14.2 volts....around 65 amps at 800 RPMS
Old     (scottie4421)      Join Date: Oct 2004       04-04-2005, 12:42 PM Reply   

I installed dual batteries on my Tige. I used a perko switch and a battery combiner. A post with instructions is below:
I finally got the batteries installed and wired up. It works great!

I went with the Off/1/All/2 Perko switch and West Marine Battery Combiner setup. I wired the starting cable to the COM (common) terminal on the Perko switch and wired the positives from each battery to the 1 post and 2 post on the Perko switch. The 1 post is my starting battery and the 2 post is my accessories/backup battery. I wired the negatives from both batteries together using a negative battery cable, and tied the negative cable from the boat into this as well.

The Battery Combiner is hooked up according to it's instructions. It's simple, just hook each red wire to the positive on each battery and the negative to the negative on one of the batteries and you're all set.

I tested the whole thing out and everything works perfectly. Now I can switch between battery 1 and battery 2, and the battery combiner takes care of charging both batteries when the engine is running, regardless of which battery is being used as the starting battery.

If anyone else is interested in doing this, you'll need:

1 Perko switch (Off/1/All/2)
1 West Marine Battery Combiner
1 Battery
1 Battery Box
2 positive battery cables
1 negative battery cable
4 self-tapping screws for mounting the Perko switch
2 self-tapping screws for mounting the Combiner status LED

Be sure not to swith the Perko to OFF while the engine is running, this will toast your alternator.

Thanks a ton for the help!

Last edited by scottie4421 on 11-01-2004 at 09:35 AM

Last edited by scottie4421 on 11-01-2004 at 09:35 AM

Old     (dgoose)      Join Date: Feb 2005       04-06-2005, 9:47 AM Reply   
I am going to install the isolater type because then you don't have to remember to turn the swicth on and off and what battery. It's automatic. the isolater will only charge one battery at a time (the weekest one) and will not over tax you alt. That is if you try to charge two batterys at once, the alt will be putting out its max amps and will take the life of the alt down. just my 2c
Old     (scottie4421)      Join Date: Oct 2004       04-06-2005, 11:38 AM Reply   
I didn't know an alternator varied it's output. In my case, the alternator is only attached to one battery. The West Marine battery combiner senses that this battery is being charged and combines the batteries to allow both to charge.

How would the alternator know that it's charging 2 batteries instead of 1? Just curious...I've never heard of shortening an alternator's life.

Also, the switching on my setup is really not a burden. The only time I need to switch is when I'm hanging out listening to the stereo for extended periods of time. And even then, I don't have to harm done if I accidentally drain the battery.
Old     (rodmcinnis)      Join Date: Sep 2002       04-06-2005, 3:50 PM Reply   
Richard: What is your reason for wanting to add another battery? Your answer may change how I would recommend installing the second battery.

Two things will establish how much current the alternator puts out: Engine RPM and the voltage regulator.

At low RPMs the alternator just can't develope much output. It generally requires the engine to be turning 2000 RPM or more before the alternator will reach full output potential.

It is the job of the voltage regulator to throttle back the alternator when the voltage gets high enough. Unless you have a "smart" voltage regulator (also known as a multi-stage regulator) it will do this just on the basis of the voltage. The current will start being reduced when the voltage reaches 13 volts and the output will ramp down as the voltage goes up. By the time the voltage reaches 14.2 volts the alternator's output should be at a minimum (which may NOT be zero).

There is nothing in the system that regulates the alternator based on the current, nor does the alternator know the number of batteries or the size of the batteries. It also doesn't know if the current it is supply is actually going to the battery or is getting used by the stereo, lights, or other equipment.

Adding a second battery, or making the battery bigger, won't directly impact the load on the alternator. Using a lot of current will. If you run the stereo for an hour and run one battery 50% down it will actually place a greater load on the alternator than if you ran two batteries 25% down.

If the alternator is getting sufficient cooling air, and the belt tension is correct, and the alternator was properly designed to start with then its life will not be significantly hurt by making it work a little more.



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