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8.5K views 44 replies 15 participants last post by  Little Ducky  
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#1 ·
I've seen several discussions on battery configurations, but I still don't get it. Any assistance would be appreciated greatly!

I have recently purchased a 2004 Sundancer 320DA. It has two Mercruiser 350 Horizons, with v drives. It has a 5Kw Kohler Generator, and 4 batteries. It appears that there are two banks of batteries, located on the starboard side of the engine compartment. A Port & Starboard bank, with two batteries in each bank, apparently they are hooked up in parallel. Not quite sure what each bank services, or what type of battery is in each bank. I gather that certain batteries should be "starting" batteries (engines/generator), and others should be "deep cycle" batteries (house load). Here's the dilemma, both engines start up just fine, but the generator won't. When I've got the 12v service on, the batteries seem to discharge at a nominal rate. The generator starts right up when the battery charger/inverter is on shore power. Still haven't tried to start it with engines running.

Do I need to replace some/all batteries? If so what kind, and where to position these replacements. I've seen "dual purpose" batteries out there, but are they as good as specific batteries in the right location? I'm not an electronics wizard, so please keep any responses simplified. Thanks for trying to make sense of my ramblings, if you need further info, just let me know.
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#2 ·
First things first. As this boat is fairly new to you, why not check out the condition of your batteries before you go any further? I would start by disconnecting all of the batteries and check them out individually with a load tester. It may be a good idea to take a pic of the cables before removing them so that you can put them back as they were before you started this exercise. Hopefully, they are all good. If not, replace them as a pair. Do not install one new battery + keeping an old battery in the same bank because your bank will now only be as good as the worst battery. Deep cycle batteries for your house load bank. Are these sealed batteries? If not, check the water level in them and only use distilled water to top them up. After you are satisfied with the condition of your battery banks you can move on to your generator starting issues. It may be as simple as the position of your battery switch if you have one. Please keep us informed of your findings.
 
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#12 ·
Great feedback, thanks! Getting all 4 batteries (only 2 years old) tested next week. Battery switches (2) are on when attempting to start. It might be that the generator is connected to the deep cycle vs. starting batteries. We'll see.
 
#4 ·
If your batteries generate enough power to crank a V8, surely they would be capable of powering a little generator starter. Always a good idea to conduct initial systems checks, like electricaldoctor said, because you don’t know the condition. But but it seems strange unless your generator is pulling from only one of the batteries which happens to be bad.

Do you get a solenoid engaging sound when you try to start the generator? Any sounds at all in the engine room?
 
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#10 ·
The solenoid does click, but not enough power to turn over. A local mechanic thinks it might be connected to the deep cycle (house load) batteries vs. the start batteries. He's going to check next week, we'll see. Thanks for the input.
 
#5 ·
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#8 ·
Thanks Fellows, great input and really appreciated. I've resorted to a marine electrician coming out to check/test the batteries (only 4, I double checked), wiring and inverter/charger, so I know what's going on, or not. Hopefully he will be able to analyze the wiring, battery types and bank positions and the destination circuits. The water level is good in all batteries (only 2 years old), and if replacements are needed, I'm going with sealed batteries. Any recommendations on which brand works best? The Generator is a replacement 5ekg installed about four years ago. It's only got 36 hours on it and the solenoid does click when attempting to start. When it runs, it's like new.
 
#11 ·
I've gone two rounds of replacing boat batteries with Duracell batteries from Batteries Plus. They are made by Dekka. There are gobs of threads around these parts addressing the different types and brands of batteries. From a price/performance perspective it's hard to justify anything other than lead acid. But it's also hard to compete with the bling and ease of install (weight) of the AGM and/or gel setups.

I'll summarize what I've come away with after hours of reading on this site on batteries: 1.) replace all of your batteries at the same time for max peace and happiness, 2.) replace them all with "combo type" batteries - starting/deep cycle as there aren't many true "deep cycles" out there, 3.) size them based on how long you'll be on the hook (Group 27 is probably perfect for 80% of the casual users in sub 40 footers) and a soft 4.) the more sophisticated battery chemistries lack ROI (flame away :):)).
 
#13 ·
If that is the case, I would not have the generator connected to the house bank. It would not surprise me if your load tests show that the house batteries are in bad shape.
 
#14 ·
You may want to consider the following:
Battery #1 + #2 House Load
Battery #3 Engines starting
Battery #4 Generator

With this configuration, if all other batteries are too weak you will always have a fresh dedicated battery to start the generator which will send power to the battery charger. Does your battery charger have 3 charging outputs?
 
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#18 ·
Something still seems amiss. Your original photo indeed shows two banks of batteries though you have a three bank charger.

I sure wish you could find that missing battery :):) ha. As mentioned above if you do replace your batteries you should find that third charger lead and give the generator it's own separate battery. That's how your boat would have been setup from the factory.

FWIW - I once owned a 340 that had two batteries on the floor between the engines. Accessibility is horrible but if you need to find a spot for that fifth battery...it'll work.
 
#19 ·
Ask the electrician to draw up a little schematic once he figures everything out.

This could go a long way in trouble shooting at a later date.

By the way in looking at your charger above you may want to go ahead and ask the electrician to change out the charger to a smart charger. He's already going to charge you for showing up.....might as well put him to work for an hour. Depending on your boats electrical set up 20/30/40 amp service pick on of the ProMariner ProNautic Series of smart chargers to match. Your batteries will thank you.
 
#20 ·
If I'm reading your owner's correctly, it looks like the 4th battery (top, right in the pic) is added by Sea Ray when there's a bow thruster and/or genny.
 
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#22 ·
Just had a second thought, if each bank has two batteries in parallel, and the Port Bank has the two deep cycle batteries for the house load, then the Starboard Bank should have two starting batteries for both the engines and the genset since they are in parallel. Does that make sense?
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#24 ·
"...then the Starboard Bank should have two starting batteries for both the engines..." No.

The port bank starts the port engine and the stbd bank starts the stbd engine. The port supplies the house loads and the stbd supplies the helm alectronics (gps/radar...) and bow thruster (or visa versa.)

Stick with matched Deep cycle batteries all around. The house bank needs deep cycle and the bow thruster needs deep cycle. They have more than enough cranking amps to start the engines. Since you only have one battery charger, you should match the banks anyway. Don't let anyone talking you into starting batteries in a boat unless that is absolutely all they do, no pumps, backup power,... Even then I would still go with deep cycle.
 
#30 ·
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Genny should have its own battery that is isolated from the others. It should be charging when you are plugged into Shore power with the charger turned on. It should be charging when the genny is operating. This set up allows you to charge the other batteries should they become totally discharged. In that case, you start the genny, power up the charger and wait for the other three batteries to gain enough charge to crank the mains. The emergency start switch helps with this by connecting the other banks together for extra cranking power. Once you get one main going the other will start with the help of the emergency switch. You can avoid this whole scenario by taking care to not allow things to discharge to such a level that you need emergency procedures. Turn one bank off and save the other, for example, if you are one the hook.
 
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#32 ·
That
View attachment 78646 Genny should have its own battery that is isolated from the others. It should be charging when you are plugged into Shore power with the charger turned on. It should be charging when the genny is operating. This set up allows you to charge the other batteries should they become totally discharged. In that case, you start the genny, power up the charger and wait for the other three batteries to gain enough charge to crank the mains. The emergency start switch helps with this by connecting the other banks together for extra cranking power. Once you get one main going the other will start with the help of the emergency switch. You can avoid this whole scenario by taking care to not allow things to discharge to such a level that you need emergency procedures. Turn one bank off and save the other, for example, if you are one the hook.
View attachment 78646 Genny should have its own battery that is isolated from the others. It should be charging when you are plugged into Shore power with the charger turned on. It should be charging when the genny is operating. This set up allows you to charge the other batteries should they become totally discharged. In that case, you start the genny, power up the charger and wait for the other three batteries to gain enough charge to crank the mains. The emergency start switch helps with this by connecting the other banks together for extra cranking power. Once you get one main going the other will start with the help of the emergency switch. You can avoid this whole scenario by taking care to not allow things to discharge to such a level that you need emergency procedures. Turn one bank off and save the other, for example, if you are one the hook.
 
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#33 ·
Makes perfect sense, but it does not look like I have a stand alone battery for the generator. Both banks of two batteries each are connected in parallel. I've turned the boat upside down looking for another battery, just can't find it!
 
#37 ·
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Many boats purchased used have systems that have been modified by previous owners who were primarily interested in saving money as opposed to doing things correctly. You have a chance to set the boat up properly. Might cost a few bucks but no ever said boating was a cheap hobby.
 
#36 ·
My thought is that with 4 batteries:
1 battery starts one of your motors.
2 batteries start the other motor and power “the house”.
1 battery starts your generator.

You can tell which is which by following from the motors and generator back. Or if the bilge is tight and following cables is tight, you can disconnect batteries one at a time and see what doesn’t work.
 
#38 ·
I looked at his owner's manual. I started to elude to this above, so to follow up... it appears his pictures are bone stock as compared to the original setup from Sea Ray in the OM. Two battery banks, port and stbd. Each bank consists of two batteries in parallel. Each bank runs through an on/off switch. Genny is hooked up to the stbd side bank (specifically, the battery in the top, right of the pic). However, as mentioned a few times, the setup can be improved upon - but at least we know there is no "previous owner" confusion going on here.
 
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#39 ·
Mine is setup with a pair of deep cycles for one engine and half the house, another pair of deep cycles for the other engine and other half of the house, and a separate starter battery just for the genny. I also keep a spare set of jumper cables in the ER. They sure come in handy for those times swinging on the hook on marginal main batteries when you want to get up and moving to another spot first thing in the morning.

A separate battery for the genny gives you the option to always start it up and slowly recharge your main batteries - but it also gives you the option to jump a pair of main batteries to the starter's battery while the genny is up and running. This enables you to start that one engine without waiting. While that main is running, you can then hit the emergency parallel switch to start the other engine. Remember to disconnect the jumpers without shorting them.

This is all assuming that you can actually GET into the ER and access the batteries. On my model there is a large day hatch between the helm and passenger seats where I can access the entire ER. With yours, you may have to electrically raise the ER hatch - quite the chore with spent batteries...
 
#41 ·
I completely rewired my batteries on the 390 years ago. I got rid of the stock 4-battery box and built a new one out of 3/4" marine plywood and installed the following batteries.
1 - 12V. cranking battery dedicated for starting both engines
1 - 12 V. cranking battery dedicated for the windlass & generator
4 - 6V. 245 A/H golf cart batteries wired series/parallel for everything else (no problems with 4-day long weekends even without the genny)

I religiously checked the water levels in these batteries 3 times per season & after 8 years they are still going strong.