New battery purchase

Bacchus said:

I'm curious what brand your GP31s are as my plan replacing my 8Ds is to go GP31s.

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They were Odyssey PC-2150s. Odyssey may have changed their naming conventions recently, but they're probably easily found.

We had two banks of 3x; each banks started one diesel (Cummins 450s) and serviced about half of the house plus one of the bridge functions (one, electrics; the other, electronics).

I eventually changed one bank of 3x G31s to a bank of 4x Lifeline GPL-4CT 6-volt batteries in series/parallel. Reason I changed was to add capacity, upping it from an initial 300-Ah to an initial 440-Ah... because we connected an inverter (+ charger) to that bank too. The set-up still gave me enough cranking amps for that engine. Only had that for about 2-3 years, though, so can't report longevity.

-Chris

Chris,
I am happy to hear that your battery setup works well for how you use your batteries and boat! I truly am and frankly not really surprised.

As Don stated about batteries: "Take care of them as recommended and they will take care of you." This point CANNOT be overemphasized, if you expect to obtain anywhere near the potential life from most battery types. It sounds like you are doing that! Battery (accurate) monitoring is usually an important part of that puzzle.

However, I do stand by my earlier statement: "Dual purpose batteries are generally not the "best" choice for house (deep cycle) use. Deeply discharging them can lead to early failure." (Emphasis added at key points). Despite that true statement, if used in the "right" way (not (regularly) deeply discharged), and looked after as recommended, they can be workable and last for a good period of time as your individual experience attests. Another factor is the quality of the battery (following recommendations is still very important) and you bought good quality.
However, to be fair, I did find your phrasing (in the post "challenging" my first post) to be a bit sarcastic as my statement is generally accepted amongst battery experts and manufacturers, and that is "dual purpose" batteries are GENERALLY not the BEST choice to use as a house bank where deep cycling is to be expected. They can be used for that application and do fill a need for certain applications. I am not disputing what you said, just the way you said it.
I do not suggest that I am some kind of "battery guru", only that I have spent quite a bit of time reading on the subject from expert sources like Rod from Compass Marine (marinehowto.com), Nigel Calder, Jeff Cote, and various battery and charging sources manufacturers.
Optimizing battery life, charging systems, battery types, etc. can be a very complicated subject with many variables and methodologies, but the "general" information I discussed is valid (based on these sources and to a point my personal experiences), but individual results may vary

Interesting reading all — appreciate all of the info. It looks like I’m going to go with the AGM31’s - I guess what i am wondering now is if i need to with 2 per 8D’s I’m replacing or can i go with 1 cranking battery (that is how it is set up not) and 2 for the house wired in parallel - thoughts?

Again - appreciate all, just first time i had to deal with these 8D’s, all my other boats were simple - two group 27’s always did the trick...

ranger42c said:

I eventually changed one bank of 3x G31s to a bank of 4x Lifeline GPL-4CT 6-volt batteries in series/parallel. Reason I changed was to add capacity, upping it from an initial 300-Ah to an initial 440-Ah... because we connected an inverter (+ charger) to that bank too. The set-up still gave me enough cranking amps for that engine. Only had that for about 2-3 years, though, so can't report longevity.

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Chris,
Having the same engines (and boat brand) I was considering that too (or perhaps the GPL-6CT since I have height available). But I wasn't sure about the impact of using strictly deep cycle batteries for starting purposes. It certainly adds cost vs straight replacement of the Group 31s, but the extra capacity seems worth it. Is there any reason to be concerned about using these as starting batteries? I really don't want to go to the expense of wiring separate dedicated starting and house banks.

BD

Longo said:

Interesting reading all — appreciate all of the info. It looks like I’m going to go with the AGM31’s - I guess what i am wondering now is if i need to with 2 per 8D’s I’m replacing or can i go with 1 cranking battery (that is how it is set up not) and 2 for the house wired in parallel - thoughts?

Again - appreciate all, just first time i had to deal with these 8D’s, all my other boats were simple - two group 27’s always did the trick...

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Now I'm confused...
1st post you reported 2 8Ds providing house & start
Now you state now (I'm assuming a typo vs not?) set up w 1 cranking batty?

If you can isolate start from house you could likely get away w 1 GP31 for start but you would have NO back up if house was drawn down low. W GP 31s pretty common for starting and are roughly equal to one 8D in CCA / MCA.
If I were experimenting and wanted to try with only 3 GP31s I would put 2 on start and isolate 1 GP31 for house. The worst case is you lose house (lights, tv, etc) went anchored out but can still start to get home.
If 1 house is obviously not enough just add a second... at least likelihood of getting stranded reduced.
So much depends on your style and usage and is the reason why there are so many different ways to skin the batty bank cat.

BDofMSP said:

Chris,
Having the same engines (and boat brand) I was considering that too (or perhaps the GPL-6CT since I have height available). But I wasn't sure about the impact of using strictly deep cycle batteries for starting purposes. It certainly adds cost vs straight replacement of the Group 31s, but the extra capacity seems worth it. Is there any reason to be concerned about using these as starting batteries? I really don't want to go to the expense of wiring separate dedicated starting and house banks.

BD

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I hate to repeat but if you are considering AGM take a look at and compare CCA / MCA for what you are considering vs what works OK currently.
AGMs can satisfy both start & house pretty well and most mfg provide both specs. FLA you will most often get EITHER CCA or AH but not both.

Was a typo - yes, i believe the current set up is one 8D for house and the other to start - planning on climbing down there and confirming when it warms up a bit. So - was curious if i could get away with one for start and two for house. Reading your reply i guess the answer is that it would be better to go with four 31’s and split them up 2 and 2.

Thanks.

Bacchus said:

I hate to repeat but if you are considering AGM take a look at and compare CCA / MCA for what you are considering vs what works OK currently.
AGMs can satisfy both start & house pretty well and most mfg provide both specs. FLA you will most often get EITHER CCA or AH but not both.

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These are AGM. The CCA ratings for the GPL-6CT are:
68F - 1150
32F - 1025
0F - 925

Amp hours are 300 at 20 hr rate

My 6CTA 8.3 450s require 1250 CCA, so I'm assuming that a pair (of 6v pairs) would cover my needs. I just wasn't sure what impact using them for starting would have. It sounds like starting should not have a negative effect on their lifespan.

Thanks
BD

BDofMSP said:

These are AGM. The CCA ratings for the GPL-6CT are:
68F - 1150
32F - 1025
0F - 925

Amp hours are 300 at 20 hr rate

My 6CTA 8.3 450s require 1250 CCA, so I'm assuming that a pair (of 6v pairs) would cover my needs. I just wasn't sure what impact using them for starting would have. It sounds like starting should not have a negative effect on their lifespan.

Thanks
BD

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If they spec both AH and CCA I have to believe they are more than capable of doing both. I have not communicated with Lifeline specifically but have with Trojan and East Penn (Duracell + others) and both confirmed AGM GCs and GP 31 both equally capable of deep cycle and start without compromises either way.

firehoser75 said:

However, to be fair, I did find your phrasing (in the post "challenging" my first post) to be a bit sarcastic as my statement is generally accepted amongst battery experts and manufacturers, and that is "dual purpose" batteries are GENERALLY not the BEST choice to use as a house bank where deep cycling is to be expected. They can be used for that application and do fill a need for certain applications. I am not disputing what you said, just the way you said it.

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Yeah, sorry, I didn't mean to sound sarcastic...

And I did sorta miss your focus on house functions, the first time around. Where I'd agree with you anyway. I must have been having some reading comprehension problems.

Mea culpa. Or I can send a beverage, whichever might be better.

-Chris

BDofMSP said:

Chris,
Having the same engines (and boat brand) I was considering that too (or perhaps the GPL-6CT since I have height available). But I wasn't sure about the impact of using strictly deep cycle batteries for starting purposes. It certainly adds cost vs straight replacement of the Group 31s, but the extra capacity seems worth it. Is there any reason to be concerned about using these as starting batteries? I really don't want to go to the expense of wiring separate dedicated starting and house banks.

BD

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I pulsed Lifeline first, before I made that change... and Justin said I should have no worries. Partly because I was talking a bank of at least 4 batts, partly because the combined CCA/MCA rating was well about what the 6CTA's needed.

I'd have gone to the taller versions too... but didn't have the overhead clearance. It was kind of a shoehorn job even with the standard height batts.

And actually, one and a half of those was seriously buried under some structural bits, so watering FLAs would have been a real chore... one reason for going with the AGMs.

-Chris

starting batts...for starting batts, i use 2 "group 31" batts with what is called "marine connectors" flat posts with holes in them, in paralell! has worked great for years, starting our 6 cyl VOLVO 70B...clyde

guess i am still old school, i have 2 8d's and 1 4d battery...i check my water often, and do hydrometer readings too,,,u may have a bad cell which i did since the previous owner did not check the batteries, so now i am on top of them. at my previous marine job, we had many 8d's and would do weekly water checks,,,and hydro reading monthly...as always, distilled water..will i go to agm...doubtful, i can still pull and remove batteries at 62, but thats me...smooth sailing 48' almin with twin tamd60c and 1 westerbeke 8btd

DDW said:

There are plenty of threads on this, the space and mounting facilities you have may dictate different but: nobody in their right mind puts 8D in to a small trawler anymore. I have 4D and am about to replace them as well. If you can, go with 6V golf cart footprint batteries. These are lighter to move and easier to pack. They are available anywhere for replacement, and are available in 3 heights depending on space and needs - the original 200AH, taller 300AH and L16 sized 400AH. For example in Lifeline AGM the GPL-4CT, -6CT, or -L16T offerings.

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2 8Ds can be replaced with 6 L16s and they provide enough energy to start my Cat 3208. The way my boat is set up, I have an 8D to start the port battery and 6L16's to start the Stb and run the house. Odd but it works. Just have to be careful to not to drain the house bank and have cabling to start the stb engine from the port start batt.

ranger42c said:

Yeah, sorry, I didn't mean to sound sarcastic...

And I did sorta miss your focus on house functions, the first time around. Where I'd agree with you anyway. I must have been having some reading comprehension problems.

Mea culpa. Or I can send a beverage, whichever might be better.

-Chris

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Chris, if you are ever out here on the west coast of BC, I would love to share a beverage with you No harm done

Comodave's Suggestion

Comodave said:

I don’t like 8Ds for a couple of reasons. First they are really heavy. Second they don’t make a true deep cycle. I would recommend that you make 2 banks. One for starting and one for house bank. Get a good starting battery and then go with true deep cycle battery for house bank like 6 volt Golf Cart batteries. It makes your setup more complicated but it will serve as a good starting system and a good deep cycle system.

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Had Trojans on my sailboat. Great house battery. The lights will never go out -maybe get four 6-volts and link them up for 12 volt output and you will have it made. Put in LEDs everywhere you can.