Dual Battery System

I have decided to install a second battery under the bow. My plan is to install a battery isolator above the engine breaker to charge the start and accessory batteries. Run a new 6 ga wire from the alt to the isolator (disconnecting the original alternator wire) , 4 ga from the iso to the accessory battery, the other isolator terminal to the engine breaker. both battery negatives hooked together (4ga) to keep a common ground. The accessory battery ground will now serve as the dash ground, fixing the common dash grounding problems.

I have also decided to re-wire some of the factory wiring. I would like to be able to turn the key off, shutting down the engine and hour meter, while keeping certain functions available. I plan to switch the bilge pump, lights, blower, and accessory breakers to run off the new battery: auto bilge in the event of taking on water while beached or tied up, stereo for obvious reasons, lights so I don't drain the start battery if the engine is off, and blower so I can just hit the breaker to turn it on while at the ramp.

All this came about when I decided to add subs/amp and run them off their own battery, and then "while I'm at it, I may as well..."

I'm looking for any input to make my upgrade better.

I have a tendency to over think/do things from time to time. They will function with the ignition breaker on, but that also energizes the hour meter. I just thought about ending the "interlock" requiring the ignition breaker to be on for accessories to function. A lot of this wiring project also came after careful inspections of previous owners' botched wiring jobs. I have been doing aircraft electronics for the last 10 years, so that sort of thing really gets under my skin. The only cost to me was the isolator ($40). The rest of the materials I have around the shop and need a home for anyway.

I totally understand a good dual purpose battery is a simple and functional way out, but sometimes I like a little challenge of reinventing the wheel to my liking.

The calculation there is the Amperage vs length of wire. 65-85 amp service for under 5 ft requires 10 ga, 5-13 ft requires 6 ga. The longer the power wire, the greater diameter needed.

The factory wiring goes from a 10 ga from the alternator, to 2 ga to the battery. I could get by with 8 to 4, but still may bump to 6 and 2 in case I put on a high output alternator.

My reasoning for this post. I've just been going off a couple charts from different sites that pertain to alternator output and length of wire. If you have the specifics for my application, that would be appreciated. I haven't run the power wires yet, was hoping to tonight but rain may delay any progress until thursday.

I'd follow that up with "You have feet, you can walk home!"

A 2 gauge wire from the battery to the starter relay is an undersized wire. It should be 2/0 or 00 as Tim likes to express the gauge but they are one in the same. Using 2 ga wire leads to starter issues and welded contacts on the relay.

what year boat? if your adding a lot of stereo stuff then your going to need to upgrade the alterntor as well, and if it's an older model with an external regulator it needs upgraded regardless.

Josh,

Something to think about that I am contemplating is how this battery will be charged. If you're charging off the alternator, think about how much engine run time you need to have to compensate for the drain you put on the second battery. Think about the dead time during the day when you're parked, draining the battery down. I'm still considering what I'm going to do long term on mine. This year I'll have two amps. One for the sub (150W RMS) and one for the tower speakers (450W RMS). Last year I could go out 2-3 times before the "house" battery needed a charge. I'll see what it does this year. Next year I plan to get rid of the sub amp and get a 5 channel (700W RMS) to drive the in-boats and sub. This year's time allowance on the battery will determine my next step. I'm considering the following two options...

1. Switch and VSR set up or isolator of some sort (Like you're thinking).
2. On-board charger and plug it in after a day of use to charge both batteries properly, including tending.

Hawktique wrote: Okie, I'm not sure if there is a "right or best way" to do this. A dual battery tender is what my buddy uses on his fishing boat and I did contemplate that Idea. I really don't spend any time "floating" with the engine off so I'm not too worried about recharg time on the acc battery. My approach was to have a comletely independent system that would function automatically.

if you aren't using the stereo while floating and it's only on when your under way (engine on) why do you need two batteries? seems stupid too me, If the engine is running the alternator is powering everything and the extra battery serves no purpose other than to add extra weight and use up storage space. I don't understand your locgic with this one. Now if your sitting in a bay chillin listening to some tunes then yea add the battery a perko switch and call it a day. Why make something simple complicated? the alternator is more than enough to charge both batteries even if one is drained.

Josh,
FYI, CQ put a dual purpose battery in his boat and trust me he does plenty of floating around, music on, creating empties he can stick on duck decoys beaks!!! Are you sure you're not just going for the "bling" factor here? You've been spending too much time over on PN!

I used a singal group 32 battery and jammed all day long at the sand bar and never had an issue. If your running bank of amps then you could use the extra batttery, I prefered to install High end speakers driven by an amp with the proper continuos watt rating for the speakers at max volume and never looked back.

I here yea, all I ever did was fire up the boat for 10-15 minutes if we had been out there for quite some time as a safty precation, but the larger battery I had really didn't need to be charged but I did anyway to be on the safe side, but what I had you just can't walk into any store and pick one up.

Josh,

Sounds like you have it figured out for what you want, which is the key. I'm still undecided on mine, like I said. I'll see how things go this year. We usually run in the morning, sit mid day, then run again in the evening, so I'm not sure if the alternator could recharge the battery enough or not.

you know a jump pack will work just as good and is a lot easier to package in the boat's storage locker too. Trust me we've drained the house battery on the sea ray more than once and the perko switch as always isolated the starting battery, but that's and all day and late night party draining the batteries and I just don't see that type of drain on a ski boat for an afternoon with a simple single amp set up. Also the part about the batteries having the same charge or type when used with the perko switch is BS, that only comes into play if you leave the switch set to both all of the time, use the switch for what it is ment to be used for switching from one battery to the other, Start out with it on the starting battery, when you float and jam out, switch it over to the house battery, try and start the boat if it starts great if it doesn't then switch to the start battery and once it's started switch back over to the house battery and charge it back up, We've only used the switch on the both setting once when both batteries where pretty old and nights worth of bomber and after that we went to the marina and got new ones.

8122pbrainard wrote: FYI, CQ put a dual purpose battery in his boat and trust me he does plenty of floating around, music on, creating empties he can stick on duck decoys beaks!!!

My mistake-they were goose decoys and not duck!!