The Official Dual Battery Thread

[JimN]

So just to get this right, I will have it fused no more than 12" from both batteries positive connections to the relay and a circuit breaker no more than 12" from battery #2 on the positive connection to my amps? Thanks for all the help on this.

Think about what would happen if the positive cable is somehow cut and shorts to ground. With only one side protected, the other battery will send everything it has to ground. A cable will dump a lot of current when this happens and if it exceeds the cables capacity, the resistance causes the cable to get hot and if there's no way to cut the current flow, the insulation will burn and take the boat with it. The only time this will stop is when the wire is thin enough to fuse, which breaks the connection.

Personally, I like breakers. They can be reset, they can be opened when work is done to the system and if it opens, it doesn't cost $8 to buy another one.

[Patrick Hardy]

So just to get this right, I will have it fused no more than 12" from both batteries positive connections to the relay and a circuit breaker no more than 12" from battery #2 on the positive connection to my amps? Thanks for all the help on this.

[TallRedRider]

I was at a MC dealership / parts dept. yesterday looking at batteries and was told that MC is now installing and recommending that only Starting/cranking batteries be used in multi battery systems. I thought that was weird, no deep cycle batteries were even sold there. Isn't that defeating the purpose of the different battery types? Anyone else hear this? Your thoughts on running starting batteries for your stereo systems?

In reality there is probably not much difference in the batteries, but I think if you kill the batteries often, a deep cycle makes more sense, and should be able to withstand the full drain more times than a cranking battery. Whether that is true in 'real life' is a little uncertain to me, but I would do it. I am big on keeping all of the batteries the same...a deep cycle is going to start the boat just fine. Just look at the CCA and such. I would do all deep cycles.

Mine has 2 cranking batteries...no problems so far and they are 3 years old, but I know the previous owner did not tax the batteries the way I do. Most of my loud music is only when the engine is on, so although I flow a lot more power through them, they do not get fully discharged.

Hey- nice Vette!

The fuse or breaker should be no more than 12" from the positive battery post. That's according to the MECP training and long experience with seeing burned vehicles. Overly cautious means still alive, in a lot of cases.

Agreed. Do the fuse.

[JimN]

I am also installing the battery relay - a PAC 200- per Diesel's dual battery System thread. I have a couple of ?'s. 1) in Diesel's first diagram he shows no fuses in the connections between the batteries positive post and the relay - page 1 / diagram 1. But in the instructions that came with the relay they show it fused at both connections per the diagram below. Is that being overly cautious? or is that something Diesel forgot and I should do? 2) I was at a MC dealership / parts dept. yesterday looking at batteries and was told that MC is now installing and recommending that only Starting/cranking batteries be used in multi battery systems. I thought that was weird, no deep cycle batteries were even sold there. Isn't that defeating the purpose of the different battery types? Anyone else hear this? Your thoughts on running starting batteries for your stereo systems?

Hey- nice Vette!

The fuse or breaker should be no more than 12" from the positive battery post. That's according to the MECP training and long experience with seeing burned vehicles. Overly cautious means still alive, in a lot of cases.

[Patrick Hardy]

I am also installing the battery relay - a PAC 200- per Diesel's dual battery System thread. I have a couple of ?'s. 1) in Diesel's first diagram he shows no fuses in the connections between the batteries positive post and the relay - page 1 / diagram 1. But in the instructions that came with the relay they show it fused at both connections per the diagram below. Is that being overly cautious? or is that something Diesel forgot and I should do? 2) I was at a MC dealership / parts dept. yesterday looking at batteries and was told that MC is now installing and recommending that only Starting/cranking batteries be used in multi battery systems. I thought that was weird, no deep cycle batteries were even sold there. Isn't that defeating the purpose of the different battery types? Anyone else hear this? Your thoughts on running starting batteries for your stereo systems?

[JimN]

I'm using the "dumb" relay (Diesel's system). The only battery I currently have is the factory starting battery. I have amps already wired to it (starting battery). Is there any reason that I can't leave the ground cables running from the amps to the factory starting battery? It sure will save a lot of hassle.

As long as there's no resistance while the audio system is on, it shouldn't be a problem. The resistance doesn't matter as much at rest but when current is flowing, any resistance will cause a voltage drop, which will be made up wherever possible. This opens the door for ground loops and noise, usually pops/clicks when flipping switches and alternator whine.

The best way is to wire the audio system + and - cables to whatever battery is supplying voltage/current to it and connect that battery to the switch, with a heavy ground cable to a common location for all batteries.

[BriEOD]

It shouldn't matter. IMO.

[bxroads]

I'm using the "dumb" relay (Diesel's system). The only battery I currently have is the factory starting battery. I have amps already wired to it (starting battery). Is there any reason that I can't leave the ground cables running from the amps to the factory starting battery? It sure will save a lot of hassle.

[TX.X-30 fan]

Brutal. What, you got down to 30, once? We didn't get over 20 degrees for 45 days. We also got over 36" of snow in December alone. Lake Michigan was frozen out to 100 yards from shore.

Look like someone needs a Snuggie!

We have been freezing 3 or 4 times I'll have you know.


I'm not sure I'd ever get laid again if I wore that thing.

[sand2snow22]

I believe its 52 water right now, we have had a brutal winter.

I'd be in a drysuit

[JimN]

No off season I'm a pu$$y about cold water. I getting the spring suit ready for the next warm Saturday OK.

I believe its 52 water right now, we have had a brutal winter.

Brutal. What, you got down to 30, once? We didn't get over 20 degrees for 45 days. We also got over 36" of snow in December alone. Lake Michigan was frozen out to 100 yards from shore.

Look like someone needs a Snuggie!

[TX.X-30 fan]

You have an off season? That's due to lack of water, right

No off season I'm a pu$$y about cold water. I getting the spring suit ready for the next warm Saturday OK.

I believe its 52 water right now, we have had a brutal winter.

[brucemac]

i don't get it. what's the difference between that and a seperator?

[TX.X-30 fan]

Gotcha, I do it different even though my starter battery is a stand alone. With the echo charger is bleeds back a trickle to the starter if it senses a drop in the starter battery charge. I get a flashing green light when its charging the starter batt and a solid light when that batt is full.

I have a problem only when the whole system drops below 11.5 amp output, the stereo batteries will output 12 until the are almost fully discharged. That is what gives me the hours of tunes floating. I spent more on the two stereo batteries instead of doing a row of cheaper batteries.

I have posted the setup before and its bulletproof.

[Sodar]

Where are you using the relay, I missed some of this earlier obviously. yes perko has been fine, hell it does not do much to screw up. I do use a trickle charger in the off season and a few time during the summer if we hammer the batts and head back in with no time to recharge them.

Noted.

The isolator will be used to isolate my stereo battery from my starter battery. It automatically connects the two batteries in parallel when it senses a charge and disconnects it when there is not.