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Old 28-03-2016, 19:58   #1
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12 volt 8D battery vs 2 - 6vlot batteries

I had an issue with batteries ever since I bought the 1989 Carver 3607.

I replaced the 3 deep cycle 12 volt batteries but still had issues.

Then while in for bottom painting the mechanic suggested that I put in an 8D battery for the house and that would solve my problems.......but it didn't.

Still issues with no battery power after 24 hours.

I have since been told that 8D's are meant to be used as a starter battery not a house and that I should have gone with a pair of 6 volt batteries.

What are your thoughts as to this issue as it is getting close to launching time.
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Old 28-03-2016, 20:11   #2
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Re: 12 volt 8D battery vs 2 - 6vlot batteries

First, you need to figure out what 12V loads you have, how much power they're drawing, the battery capacity, charger capacity and what state of charge you manage to achieve.

Until you do a power audit you're just spitting in the wind. No way to answer why you're batteries keep running down.

Regarding the 8D, that is a size designation, not a designation of whether or not the battery is designed for starting or house loads IE a deep cycle battery.

All that being said, a true deep cycle, 6V battery like a Trojan T105 is designed for house loads and tolerates deep discharges much better than a starting battery. This type was my choice for batteries on my boat. Also they are a whole lot lighter and easier to handle than an 8D.

So a few questions.

1. What 12V equipment are you running on your boat? Fridge is usually one of the highest drawing bits.

2. How are you charging your batteries? Size/capacity of the charger?

3. How are you monitoring the state of charge of the batteries? Do you have any kind of battery monitor, amp meter or similar?
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Old 28-03-2016, 20:12   #3
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Re: 12 volt 8D battery vs 2 - 6vlot batteries

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Originally Posted by 1000 islands View Post
Still issues with no battery power after 24 hours.

I have since been told that 8D's are meant to be used as a starter battery not a house and that I should have gone with a pair of 6 volt batteries.
.
What Is A "Deep Cycle" Battery? Photo Gallery by Compass Marine How To at pbase.com

After 24 hours? How big is your daily draw in amp hours? i.e., what is your energy budget?
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Old 28-03-2016, 21:01   #4
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Re: 12 volt 8D battery vs 2 - 6vlot batteries

Do you not care about your back, are you intimately friendly with a back surgeon, do you have a gorilla or two as friends. If you do, then get an 8D. Those damned batteries are so heavy they are likely to result in dire consequences trying to move them let alone haul them out of the boat. There are a number of different types of 6v batteries besides Golf Cart Batteries that will give you tons of amperage when connected in series and/or series/parallel that can be moved without doing damage to your body.

Yes, 8D's are starting batteries for large diesels.
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Old 28-03-2016, 21:29   #5
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Re: 12 volt 8D battery vs 2 - 6vlot batteries

one 8D or 2 golf carts you will have the same issue. as they are about the same size.


figure out what is killing them. or why you are using so much power.


a 36' boat probably needs 6 golf carts for a house bank.
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Old 29-03-2016, 06:27   #6
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Re: 12 volt 8D battery vs 2 - 6vlot batteries

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Originally Posted by smac999 View Post
one 8D or 2 golf carts you will have the same issue. as they are about the same size.

figure out what is killing them. or why you are using so much power.

Yep, pretty much. A typical 8D is not truly a deep cycle battery, and will offer about 245 Ah. A pair of 6V golf cart batteries would be deep cycle but would still only be giving about 220 Ah at 12V. Not too dissimilar. (And all that is max, so really only about half of either would be routinely available assuming a goal of no less than 50% depth of discharge.)

1000, you didn't say much about circumstances. You've got twin engines; gas or diesel? (Latter usually need more cranking amps.) Does each engine have it's own start battery(ies)? And if so, are you only talking about the battery bank that services the house loads?

Anchored out? Running a fridge or two? Electronics suite always turned on? Inverter loads?

Genset available? Battery charger working? How often do you re-charge?

Or at the dock? Plugged into shorepower? Same situation?

And so forth...

Sounds like its not about the batteries (type, size) per se, but instead about the loads, charging regime, etc. Although your loads might end up suggesting you need MORE battery, no matter which kind.

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Old 29-03-2016, 13:27   #7
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Re: 12 volt 8D battery vs 2 - 6vlot batteries

Quote:
Originally Posted by 1000 islands View Post
I had an issue with batteries ever since I bought the 1989 Carver 3607.

I replaced the 3 deep cycle 12 volt batteries but still had issues.

Then while in for bottom painting the mechanic suggested that I put in an 8D battery for the house and that would solve my problems.......but it didn't.

Still issues with no battery power after 24 hours.

I have since been told that 8D's are meant to be used as a starter battery not a house and that I should have gone with a pair of 6 volt batteries.

What are your thoughts as to this issue as it is getting close to launching time.
JMHO, I am an advocate of 8Ds for stating batteries but golf cart batteries are better for house batteries. On the other hand look at the price differential. A couple of 8Ds may be cheaper than four 6Vs and throw them away periodically. If you want an 8D go to a supplier for semis not marine.
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Old 29-03-2016, 15:25   #8
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Re: 12 volt 8D battery vs 2 - 6vlot batteries

As Ranger42c mentioned, is your inverter On? If it,, and you are not connected to shore power, your house bank is powering your coffee maker, your computers, your microwave oven, etc, etc. When you are connected to shore power, if you have system like mine, the 120v power is drawn from the 12v batteries which are constantly monitored and charged by the shore power connection. When we are not shore power connected. We switch off the 120v main and live with our 12v system.
Do you think the 120v drawdown could be causing your batteries to disccharge?
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Old 29-03-2016, 15:46   #9
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Re: 12 volt 8D battery vs 2 - 6vlot batteries

When I bought my 38' boat it came with a used 8D battery. I thought I did everything right to keep it in good shape, but it was dead in 2 years. I bought a new Interstate Marine 8D and got instructed on how to care for it properly. Essentially, if you're on a mooring and you only run your engine to get in and out, you probably will be like me and kill your new battery in short order. My new one was dead in 3 years. It's not the battery, but how you treat it. I'm going to buy 6V batteries because I'm tired of breaking my back getting a 120# battery off the boat, in a dingy and up the ramp. I'm also going to get a solar charger to keep it up to snuff. My starter battery has a small solar charger and is doing great. I need to be able to top off my house bank to avoid killing it again.
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Old 29-03-2016, 17:57   #10
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Re: 12 volt 8D battery vs 2 - 6vlot batteries

I agree with what you've received so far, Energy budget first, then if that's OK see if there is an unusual draw, (short) in your system. If you are running out of power you most likely have an unbalanced budget. When you do you budget you should not be below 50% of total capacity before recharge. This will add battery life. After that size matters. 6 volts typically have slightly more amp hours available and are lighter than D8s and easier to manage. No need to go with brand name Trojans, the knockoffs are just as good and have the same warranty's, shop arround. For my money, 6 Volts in series are the way to go. A pair of knockoffs is less than an 8D in most cases. Save your back.
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Old 29-03-2016, 20:42   #11
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Re: 12 volt 8D battery vs 2 - 6vlot batteries

I can answer this question for you. I used to install inverters. I tried 8d's 12 volt deep cycle and golf carts. The gold carts out perform all the others by far. The 8d and the golf cart perform the same the first year. The difference is future performance. The 8d has about a thre year cycle used as a deep cycle. The first year 100 percent. Year 2 66 year 3 33. The golf cart will loose about 5 to 10 percent per year. A huge difference. The golf cart is designed for exactly what we need them for. Always go with them.
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Old 30-03-2016, 10:43   #12
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Re: 12 volt 8D battery vs 2 - 6vlot batteries

I have a single East Penn deep cycle 8D house battery for house loads. It handles overnight anchoring with no problems, keeps the fridge, lights and fans running. I do run the gen for about 1 hour in the mornings and about 3 hours in the evenings to cook and charge batteries. I have a 60 amp charger and switched out all the interior lights and the anchor light to LED bulbs to save on DC use. What loads do you have, what is charger capacity, do you run generator or mains during the 24 hours. I don't know that I could go 24 hours without charging from engine alternators or generator use.


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Old 30-03-2016, 11:48   #13
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Re: 12 volt 8D battery vs 2 - 6vlot batteries

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I can answer this question for you. I used to install inverters. I tried 8d's 12 volt deep cycle and golf carts. The gold carts out perform all the others by far. The 8d and the golf cart perform the same the first year. The difference is future performance. The 8d has about a thre year cycle used as a deep cycle. The first year 100 percent. Year 2 66 year 3 33. The golf cart will loose about 5 to 10 percent per year. A huge difference. The golf cart is designed for exactly what we need them for. Always go with them.
X2 on this. use batteries that are designed for large discharge, large recharge. Starting a semi isn't that. Driving around all day hitting a little white ball is. Golf Cart batteries are the best bang/buck option for house loads. (There are other advantages to use AGM or other types, but it's not bang for buck)

And 2 GC2's are definitely easier to move around.

Do a load analysis - I'll bet you find out you'd be better off with a 400+ AH bank.
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Old 30-03-2016, 12:31   #14
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Re: 12 volt 8D battery vs 2 - 6vlot batteries

I see there's no response yet from 1000 Islands so seems like we're at a stand still. Hard to give a relevant answer without knowing a little more about the overall electrical load and charging system.

Otherwise it's like asking why my car runs out of gas so soon. To answer it will depend on how much gas you put in the tank and how much gas your engine is burning.
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