2 generator cranking batteries?

TitanTn

Active Member
Jul 12, 2015
386
Chattanooga, TN
Boat Info
1986 Saltare, 1998 400 Express
Engines
454 direct drive; twin 3116TA
Ever since buying my newest Sea Ray I've been wondering about the logic of the battery setup. I have 3 batteries on the starboard side that seem to setup from the factory. One is a dedicated cranking battery for the port motor, the other two start the starboard motor and are the house batteries.

Here's where there is a little deviation. I have 2 batteries on the port side. Factory setup calls for one. The cabling for both of the batteries looks stock, but who knows. The hot wires run from the batteries into a loom that runs to the starboard side. Who knows where they go.

Last week I couldn't start the generator. Not enough juice. So here's my chance to figure out which of the two batteries is the generator battery. I disconnect one and tried the generator. Still click-click-click. Not enough juice to start. Okay. Must be the other battery. Hook number 1 back up and disconnect number two. Same thing. Click-click-click. Both batteries are weak, but they both are generator cranking batteries? I replaced the number one battery and the generator cranks fine. For now I've disconnected the second battery and will try to find something that isn't work, but for now my best guess is that both batteries are generator cranking batteries. Anyone ever see this before? Why?

One other thing. The battery I replaced is a 1000MCA cranking battery. Battery number 2 is a deep cycle battery. Just doesn't make sense.
 
I'm confused but it sounds like you don't know how old your batteries are or how they are wired. I suggest you get a digital volt/ohm meter and a pad of paper and trace the system while making notes. Then you can make some logical decisions.
 
I'm confused but it sounds like you don't know how old your batteries are or how they are wired. I suggest you get a digital volt/ohm meter and a pad of paper and trace the system while making notes. Then you can make some logical decisions.

The point is that I don't know how the batteries on the port side are wired. The behavior of how they're wired doesn't make sense and at least for me it's not as simple as testing with a meter. I did use an OHM meter to check continuity on the hot lead and I got continuity on every hot lead I touched. So this showed me nothing. I can't physically follow them through all of the looms without basically taking apart most of the battery wiring. I might get to that point but first I'm wondering if anyone has an idea as to why both of the port batteries would be connected to the cranking circuit of the generator.
 
A few things come to mind:

1. Is it possible the two batteries are wired in parallel somewhere downstream? So essentially they would be working as one much higher current battery.

2. Did you put the known good/new battery into the #2 spot and try it? If your generator starts then they are indeed wired in parallel.

3. Do you have a bowthruster?
 
A few things come to mind:

1. Is it possible the two batteries are wired in parallel somewhere downstream? So essentially they would be working as one much higher current battery.

I definitely think it is. I just don't know why someone would go to the trouble of doing this.
2. Did you put the known good/new battery into the #2 spot and try it? If your generator starts then they are indeed wired in parallel.

No, that's the one test I didn't do. It would be easy to test and I'm very confident that it would start the generator.
3. Do you have a bowthruster?

No. No bow thruster. Great thought though.
 
Something doesn't sound right here. If you have 3116 Cats, then it takes 2 group 27 or larger to crank each one of them. The typical configuration is 2 group 27 (30's or 31's) for each engine and one dedicated battery for the generator for a total of 5 batteries.
 
Something doesn't sound right here. If you have 3116 Cats, then it takes 2 group 27 or larger to crank each one of them. The typical configuration is 2 group 27 (30's or 31's) for each engine and one dedicated battery for the generator for a total of 5 batteries.
That's interesting. I don't know what typical is because documentation isn't as readily available for an Express as it is for a Sundancer. I know I've seen a bilge configuration diagram for the Express, but I can't find it now. The diagram had 3 batteries on starboard and 1 on port.

On the starboard side I have 3 batteries. They are all group 27, but as I described in my first post, the first battery is the only one that cranks the port motor. I know this because all 3 batteries were dead when I took possession of the boat. I had brought an extra battery with me just because I suspected trouble. I replaced the first battery on the starboard side and easily cranked the port motor. I then used the emergency start switch to crank the starboard motor.

So I don't know how to respond to what you describe as typical, but my setup doesn't seem to match your description at all.
 
Yup, all of my boats have two batteries per engine and one battery for generator. My current boat also has two dedicated batteries for the bow thruster.
 
I've found the bilge layout for the 400 Express. I also found a battery diagram. Neither show 2 batteries per engine. My battery bank "looks" factory and surely someone didn't change it all to reduce the number of batteries used...

The diagrams are attached.
 

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Thanks Mark. I feel like that's what mine had from the factory. 3 on the starboard side for the motors and house. One on port side for the generator. I feel like one has been added on the port side and for someone reason is connected to the existing generator battery. But everyone else is saying there should be 2 batteries per motor.
 
now this is a '98 400 DA but it can't be that much different...
 

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Here are some pics I found online of another 400 Express. Not a diesel, but at least it's an Express. My battery setup is just like this except for an additional battery right beside the single battery.
 

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I just bought a 1994 Express Cruiser with Mercruiser 502s this week. I replaced the 4 batteries that mine is equipped with and was equally confused by the layout. Mine has 3 batteries on the starboard side (from bow to stern - group 24F, group 27DC, group 27DC). The group 24F starts the port engine. The two group 27DCs wired in parallel start the starboard engine. There is one battery on the port side (group 24f) that starts the generator. The owners manual for the 1992 states the batteries on the starboard side should all be group 27s. Not sure why mine and the picture you found have a smaller battery starting the port engine.

Edit: corrected generator battery to port side.
 
Last edited:
....There is one battery on the starboard side (group 24f) that starts the generator....
Did you perhaps mean to say that the generator battery is on the port side? If so, this is exactly like my setup (except I have an additional mystery battery on the port side).
 
Did you perhaps mean to say that the generator battery is on the port side? If so, this is exactly like my setup (except I have an additional mystery battery on the port side).

Yes. Corrected original post.

This thread has been very helpful. Thanks!
 
Yes. Corrected original post.

This thread has been very helpful. Thanks!
And thank you for confirming that the 90's model Express boats are likely setup like mine with the exception of my additional port battery. Someone spent some time running the mystery battery cables through the factory loom. I still don't understand why they felt like they needed 2 generator cranking batteries.
 
Maybe the wires going forward were for a inverter added by previous owner then removed.

This is what I found in my bilge. Two very heavy cables running forward thru bulkhead, I originally thought they were for windlass. Later found the actual windlass cables and associated breaker and realized I had to find out were these cables went. Disconnected them and nothing "died". Then made a concentrated effort to trace them and they ran to a storage compartment under the cabin steps, where an inverter had once lived.
 

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