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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance
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  #1  
Old 11-29-2011
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Battery Bank Options

I currently have two 6 volt (220 amp amp hours) deep cycle batteries for the house bank and one 12 volt AGM (105 amp hours) for a starter battery.

I would love to have the room to add two more 6 volt batteries but do not have the space. Should I settle for the 220 amp hour battery bank or move the AGM starter battery somewhere else and add a 12 volt deep cycle battery to the house bank?

My electrical needs are modest for day sailing but I would like to do long weekends next year.

Thanks,
george
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Old 11-29-2011
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George,

Yours is a classic problem. One always needs/wishes for more capacity :-)

What to do depends on a few things, including the type/size of boat, the age of your batteries, the loads you expect over a long weekend and the steps you have/could have taken to reduce loads (like LED lighting), the type of charging system you have, etc., etc.

Three things to remember:

1. if possible, keep all batteries in a bank of the same type and size and age;

2. don't cycle below about 50% capacity (so, no more than about 110AH from your present bank);

3. charge the batteries fully as soon as you can (like when you return to the dock after a long weekend).

If it turns out you absolutely can't add more like-sized batteries to your battery bank, you might consider going to a different type of battery....AGM or gel. These can be cycled below 50% without harm, so you'd have a bit more capacity for your long weekends. Between the two types, and knowing only what you stated in your original post, I'd consider gels over AGMs to increase usable capacity a bit in the same footprint.

Bill
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Old 11-29-2011
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There is consensus on having all batteries of the same type. If you have an alternator to charge your batteries onboard, you ought to have a "smart" regulator that is programmed for your battery type.

If you go with a gel or AGM house bank and a "smart" regulator, like the Balmar Max Charge, you will find that your batteries will charge more quickly and be more likely to be closer to a full charge when you shut your motor off. Gels, including AGMs, can take a higher initial charge rate than liquid cells and the smart charger will allow the initial charge rate to be higher and will be more likely to keep from overcharging your batteries.

We had a conventional regulator for many years and finally switched over to a Balmar Max Charge regulator. It made a huge difference for the better. We also switched to AGMs from gels last year, but its too soon to know it that made a big difference. They did seem to hold up better, but they were new batteries and we had also switched our cabin lights over to LEDs to reduce power consumption at anchor.
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Old 11-29-2011
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You can discharge golf cart batteries to 80% depth of discharge, but you will only get 225 cycles before the battery dies. If you always do 50% depth of discharge you get 750 cycles. This will vary some with the type of construction and alloys in the lead. So you can discharge greater than 50% on those times where you do a weekend. Unless you have a 12 volt refrigerator, or some other item that needs lots of power, I doubt you well get close to this. You need to make an estimate of how much power you will use on a weekend. Also, if you have flooded cell batteries take a hydrometer and see if you can charge the batteries all the way. If the batteries sit discharged, or partially discharged, sulfonation can take place and the batteries will not be fully charged. If you charge the batteries as much as you can and the hydrometer still shows only a partial charge, or near dead, you will need new batteries. Be careful with the hydrometer as any stray drops from the pickup tube will eat holes in your clothing, or cause skin irritation. Keep a plastic cup handy for the stray drops. Also, if you have the flooded cell battery, you can add water, but do it only after charging as water floating on the top of the cell will give a lower reading that what is really there. You have low maintenance batteries that have no way of adding water or for using a hydrometer, you can also check on sulfonation by taking a voltage reading with a very accurate voltmeter after the battery has sat six hours since being charged. If you cannot charge the batteries while at the dock, or by charging with the engine, then get solar panels with a charge controller. If you charge at the dock make sure you have a marine charger that isolates the batteries from the common ground for AC 120 volt power else you can have electrolysis that eats up the metal on the boat very fast.

Last edited by LakeSuperiorGeezer; 11-30-2011 at 12:02 AM.
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Old 11-30-2011
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You could forget the extra batteries and go to LEDs : Keeping the weight down. I run only two batteries, 1 house & 1 starting . I find it works -Dale
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Old 11-30-2011
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Quote:
Originally Posted by gbm4th View Post
I currently have two 6 volt (220 amp amp hours) deep cycle batteries for the house bank and one 12 volt AGM (105 amp hours) for a starter battery.
How are they charged? I presume the 6V batts are wet and you said your starting battery is AGM?

Quote:
Originally Posted by gbm4th View Post
I would love to have the room to add two more 6 volt batteries but do not have the space.
Common issue. How deeply are you currently discharging your 220Ah bank? Do you have a battery monitor to know for sure how deeply you're discharging?

Quote:
Originally Posted by gbm4th View Post
Should I settle for the 220 amp hour battery bank

This can't be accurately answered unless we know your average depth of discharge and have more information on your use.

Quote:
Originally Posted by gbm4th View Post
or move the AGM starter battery somewhere else
Always an option if you need to.

Quote:
Originally Posted by gbm4th View Post
and add a 12 volt deep cycle battery to the house bank?

That would not be the best choice. As others have said batteries wired in permanent parallel banks should be installed at the same time, from the same date code, same lot # and same model. All batteries have slightly different internal chemistries, that also change with age. You want to wire contiguous banks with all the same brand, model and age batteries for the longest life. They also need to be wired correctly and loads should be pulled across a bank not off of one end. I take it a step further when buying batteries for customers and myself and put an $800.00 analyzer on them to find the best matches to put into a contiguous bank.

Quote:
Originally Posted by gbm4th View Post
My electrical needs are modest for day sailing but I would like to do long weekends next year.

Thanks,
george
The best money you could spend at this point may be a battery monitor. The Victron BMV-600 is an excellent value and can SAVE you money..

Personally I would not make the switch, for your described use, to AGM or GEL. Most every AGM maker, Lifeline, Deka, Trojan etc. suggests a max depth of discharge of 50%, just like wets, and even at 50% DOD I find AGM's generally speaking still last less long than good old deep cycle wets do.

In the beginning AGM and GEL makers did suggest, and in some cases still do in marketing materials that don't tell the whole story, that AGM & GEL can be more deeply cycled. In reality they found out that was just not the case. GELS will still get more cycles than AGM when deeply cycled but you are paying up to 3X the cost of wets that will come darn close and should easily exceed 5 years use..

GELS can certainly be the longest lasting batteries but also the most difficult to keep properly charged and when compared to a decent quality deep cycle wet battery like a Deka/ East Penn, Crown or US Battery they cost about 3X as much.

Switching to AGM and GEL may require a large upfront expense on not just batteries, often 2 to 3 times more than deep cycle wets, but charge regulation as well if you don't already have it. Charge regulation & alternator upgrades can get very costly especially when added to the cost of a bank of "gourmet" batteries.. For "occasional weekend use" I find this money could be better spent on conservation such as LED lighting, or, if applicable, dedicated 12V devices as opposed to using an inverter..

If you can get us some more usage info and we can better assist you in getting the most bang for the buck in the space constraints you have. You may find that 220Ah's, or more accurately, 110Ah's, is enough for what you want to do.

If you find you do need more Ah's, 3 group 31 Deka deep cycle batteries with 105Ah each, or 315 Ah's for the bank, can be had these days for under $250.00 for all three batteries. With some 12V group 31's you can get as much as 390 Ah's with just 3 batteries..

Figure what you need first and consider a battery monitor, under $190.00.....
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Last edited by Maine Sail; 11-30-2011 at 10:33 AM.
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Old 11-30-2011
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Monitor.

Quote:
Originally Posted by Maine Sail View Post
How are they charged? ... consider a battery monitor, under $190.00.....
I agree with Maine Sail, all his points from beginning to end. I have never owned a battery monitor, but I think it would give you a good idea of amp-hour usage. I would still use a hydrometer every month because of internal battery discharge which the monitor would not track. A battery can discharge enough in a few months just sitting there to cause sulfation. To avoid using the hydrometer, I would get a 135 watt solar panel for battery charging. It should be enough to charge the battery between weekends, about 330 amp-hours (Probably a little less because of a controller needed to prevent overcharging). You could go with something smaller depending on how much battery charging you have from other sources such and engine or shore power. Maybe a 45 watt panel would do it which gives about the same amp-hour in a week as you would use if you went to 50% depth of discharge. I assume 5 hours per day of full power from the solar panel because of sun angle and the night time gives nothing.

Last edited by LakeSuperiorGeezer; 11-30-2011 at 12:43 PM.
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Old 11-30-2011
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Thanks for the comments and suggestions.

I just had my engine replaced and a new smart regulator installed with a 65 amp alternator (the largest that would fit a Beta Marine 25). Somehow my Balmar alternator disappeared with the old engine.

I have installed some interior LED lights and am in the process of installing LED navigation and anchor lights.

I have a Victron 602 battery monitor I need to install.

I have a 130 watt solar panel with MPPT controller that needs to be installed.

No refrigeration. Just lights, stereo, navigation equipment and a Lectrasan head. I try to keep the batteries at full charge every time I go down to the boat with a marine charger.

It sounds like I should keep my current battery bank and monitor usage next summer. If I am stressing the house bank I can go with three 12 volt marine batteries (Sam's Club).

From what I have read, Gel and AGM batteries have a higher acceptance rate and may burn out my alternator.

Thanks again,
george
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Old 11-30-2011
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Unless you run your motor for long periods on a regular basis, the higher acceptance of AGMs over gels, which is higher than liquid cells, is attractive for sailboats. Yes, you need to have a smart regulator to take advantage of the higher acceptance rate, but you also need the smart regulator to keep from overcharging--whatever your battery chemistry.

MaineSail may have a point on the cost-benefit of liquid cells. if you are truly budget-driven, you can skip the LEDs and the monitor and use a regular voltmeter to avoid deep discharges of your liquid batteries. Switching over to LEDs is a great conservation move, but I would put them in the "gourmet" category until the prices drop quite a bit more.
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Old 11-30-2011
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The last item I would skip would be the Victron battery monitor. A voltmeter cannot give you the same information.

If you were to go with AGM batteries temp sensors for the alternator and ideally batteries as well should be installed. The larger the bank in AH's the more important this is.

65 amp is the largest? I would think a small frame 100 amp alt should fit fine.
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