Dual Battery Wiring Question... ground wire to nowhere?

[SoldTheBayliner]

I have a dual battery set-up in the boat I bought at the end of the season last year. I'm unfamiliar with the boat and with dual battery set-ups in general. It had two dead batteries, and I put one new one in and took the #2 battery out last year. I just ran it on one. I just bought a second battery to put in the #2 spot, and realized that I didn't know which was the ground wire and which was the hot wire (same color, exact same wire). There is just two wires going to the #2 battery. I followed the one that I suspected to be a ground, and was surprised to find that it runs all the way up to the front of the boat (under passenger seat area) and just stops. It's not attached to anything. The other one (must be the hot wire) runs up the other side of the boat towards the dash. Neither one goes to the Perko switch (is this normal?).

I know they are linked, because the dead one sucked the life out of my new one when I first put it in (before I got smart and pulled out the dead one last year). So I'm assuming the hot wire from this #2 battery goes forward to the dash, and then back to the switch from the dash pod?

And is it normal to have the #2 battery ungrounded? Seems like an obvious no to me? Can someone explain the basics of how the second battery ties into the whole dual battery switch/system?

Thanks......

[Luke 'Lukey' Thomas]

Hmm, thats not how my dual battery setup is hooked together. It sounds like you've got them in series, thats the only explanation I can think of as to why the one battery would drain the other. Do you have a battery selector on the isolator? Or is it just On/Off?

[TallTex]

Does not sound correct. Check out a youtube channel to see "best practices" of having a dual battery setup, any application. Remember to up the size of your battery terminal cables if upping the amps of an high amp system. Do not burn up a new alternator with too small of battery cables or weak battery or other things that increase resistance of system. They need to be isolated from each other, in addition, you may think about installing an on-board trickle charger/batter desulfater to keep any/all batteries charged and fresh. (never have a battery die again) I like battery minder chargers desulfater units, reasonable priced and can handle multiple batteries at same time. http://batteryminders.com/

http://www.youtube.com/watch?v=RlNTqEqRF0Q

[scottb7]

I just played with mine last weekend. Wires to batteries positive are red. You can easily trace it if you unscrew unit from side of boat and look at the wires and carefully trace where they go.

[gride]

what gauge wire was running up to the bow? i have some crap 8 gauge that was factory amp cable that i havent taken out yet that runs the same way as what you're talking about. the perko(Assuming thats what you have) is very simple to wire the second battery. they have manuals on their website. but, the 2nd battery HAS to have power and ground to work. typically the batteries will share a common ground on the switch, while the positive wires go to each respective post. not using seperate color power/ground sucks. i just realized the system in my truck has the same color for everything and it just makes things slightly more cumbersome when messing with it.

[TX-Foilhead]

I sure wouldn't plug in another battery until you know what wires go where even if you have to remove a few interior pieces to check. I'm going with it being something done for a stereo at some point, but I've seen some very poor stereo wiring when people try to DIY things they don't understand.

[gride]

FYI: a run from battery 2 up to under the observers seat for amps needs at least 4 gauge power/ground wire and you'll still probably have a bit of voltage drop.

[Chexi]

To clarify, you should not have any ground wires run to a Perko. You have the alternator line going to what I think is the center post and the side posts being used for the respective positives on each battery. Your negative battery terminals are connected to eachother, with the ground running from your main battery to the engine ground.

Personally, I prefer the Blue Seas isolator combiner system and just installed it in my 2000 SAN and added my audio battery. It's about 3 to 4x the cost of a Perko, but having the automatic relay to allow for automatic charging of my audio battery is worth it to me. It makes for a "smart" system.

For reference, I have alternator running to main battery positive. I have engine ground running to main battery negative. Main battery positive running to post 1a on switch. Post 1b on switch runs to Relay post A. Post 2a on switch runs to distro block. Post 2b on switch runs to Relay post B. Distro block grounds to main battery negative. Positives of in-boat speaker amp runs to Distro block and ground at main battery. Head unit positive runs to distro block and grounds at main battery (or distro negative terminals). Positive of tower amp runs to audio battery and is fused at the battery. Negative of tower amp runs to audio battery negativ, which is connected to main battery negative. I have to check for ground loops, but so far have not noticed any. Ballast Pumps positives and negatives run to distro block positives and negatives. Probably pretty confusing. You have to draw it out.

This setup allows me to play my audio with the boat otherwise completely off. I just turn the battery switch to on and then turn on the head unit. Remote on of head unit powers up both amps. All audio equipment is powered off the audio battery, so I have no draining of the starter battery when playing audio (or using ballas puppies). The starter and other house lines all run off the starter battery using the factory switch at the driver kickplate and keypad.

[scottb7]

As chexi said when i looked at mine there were no ground wires to perko, all positives. here is what i thought was interesting, but probably just me being dumb. they had distribution block from stereo amps going not to battery one or two but to the common. at first i thought this was wrong and was going to move it. but then i got to thinking that then i would have to choose which batter would be for stereo and which would be for main/starting. and it was going to be a tough decision because one was 4 years older then the other, and that the older one was the good one....

but i then i got to thinking that the way it worked now was that whichever battery i choose became the one the amps(stereo) pulled from. so i could when i parked boat to listen to music choose either of the two batteries. that would get used and the other battery would remain "isolated". then when I start boat I could switch back to both and have both be charged or just charge the one i had used for the stereo. And next time I could isolate the other battery. So in essence i had a dedicated starting battery by choice of which one i isolated.

maybe that's always how it works and i just now finally understand it...it just seems better that way then picking one battery to put stereo amps on and then having it stuck that way. am i wrong?

[Neverenough]

Sounds to me like the prior owner had an amp wire ran to the front. Which you would need both positive and negative. Quick note don't just add one battery. Adding one new battery will eventually run down the old one. This may sound crazy but I take a volt meter with me when I buy new batterys. Check them to see how close they are. I buy the two that are at the closest build date and voltage. Seems to help them last longer.

[Chexi]

As chexi said when i looked at mine there were no ground wires to perko, all positives. here is what i thought was interesting, but probably just me being dumb. they had distribution block from stereo amps going not to battery one or two but to the common. at first i thought this was wrong and was going to move it. but then i got to thinking that then i would have to choose which batter would be for stereo and which would be for main/starting. and it was going to be a tough decision because one was 4 years older then the other, and that the older one was the good one....

but i then i got to thinking that the way it worked now was that whichever battery i choose became the one the amps(stereo) pulled from. so i could when i parked boat to listen to music choose either of the two batteries. that would get used and the other battery would remain "isolated". then when I start boat I could switch back to both and have both be charged or just charge the one i had used for the stereo. And next time I could isolate the other battery. So in essence i had a dedicated starting battery by choice of which one i isolated.

maybe that's always how it works and i just now finally understand it...it just seems better that way then picking one battery to put stereo amps on and then having it stuck that way. am i wrong?

This is correct. If you use a Perko, you can select which battery(ies) is/are being used. You can use battery 1, battery 2, or both. So, you could run off battery 1 for everything while underway and then switch to battery 2 when you are parked and listening to tunes... or vice versa. What this system does not provide is charging of the isolated battery by the alternator when the other is selected. In my example, you would not be charging battery 2 at all when underway. It forces you to either run both at the same time when underway or to shore charge the one you run down when parked. Having a relay allows for charging the secondary battery when the primary is within the optimum charge range. This also (I think) allows you to safely use 2 batteries that are not identical and that are not close build dates. For example, I use a Sears Platinum (military spec made by Odyssey) for my starting battery as well as all the stock function of my boat. On the other hand, all my audio runs off an Interstate Deep Cycle that I happened to have from my old 99 Air when I bought it. The Interstate should not be able to kill my Platinum, because the relay only opens when the alternator is charging and the primary battery is golden. I will post pics soon (of all my projects this year)... once it stops raining.

[scottb7]

Yep just like you said....I just double checked mine. i mispoke it is not perko. it is bluesea 9001e http://bluesea.com/products/9001e this like many units has make before break technology which allows switching between 1, 2, or both while under load, just not to off. So when i listen to music off of battery 1, i keep battery 2 isolated to start the boat. then per instructions i switch 2 both and charge both while running. Depending on how run down battery 1 got it may not fully charge. I should just leave it on 1 and only bring 2 online if it doesn't start. It would be nice to have the relay so that it would switch the charge depending on where needed. If you get a chance to share more info on the relay let us know.

kind of off topic...i notice that on starboard side the battery sits flat but on port side it is tilted, tilted like slanted down toward center of boat...i think i might have to wedge a piece of wood or something in compartment on side of battery box to level the port side. do you think it matters much if they are level or not?

It would seem to me that these take beating bouncing around but maybe they don't move around that much. Or maybe it does not matter.