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Hello,

I was wondering if you guys could weigh in on what are the advantages and disadvantages of the different types of marine deep cycle batteries: AGM, Gel, and Wet Cell. Thanks!
 

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Wet...cheap, rugged, most bang for the buck. Limits: Maintenance, subject to sulphation, can only charge or discharge at 15-20% of capacity so it takes a long time to charge after discharge. Must be EQ'd once every month or two to avoid sulfation. Self discharge of 10-15% per month makes winter charging or storage necessary.

AGM...rugged, no maintenance, can be charged 2 to 5 times faster depending on model, can be mounted in any position. Sef discharge rate of about 1-3% a month. Downside 3x more expensive, requires PRECISE charging system and MUST be brought back to 100% state of charge at least every week or two. Generally about 20% less cycle life than an EQUIVILENTLY built wet cell. They are not economical compared to wet cells EXCEPT in full time live aboard situations where the charging time advantage pays for the price difference in fuel savings and maintenance.

Gels...same advantages as AGM's but can be discharged deeper without damage. Cannot take the same level of charging current as an equivilent AGM but better than wet. Extremely sensitive to over charging and require different settings on an external regulator and battery charger. Can be quickly destroyed if overcharged. Not widely used in marine applications anymore.

Note...there are big differences in quality and price between various brands in the same TYPE batteries as well. The Wal Mart Special Wets are not the Same as Surette Wets.
 

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After years of dealing with wet cells and thier maintainence as well as their longevity we put in 6 (6 volt) Lifeline AGM Batteries this year. As Cam said low maintainence, can be put on thier sides. Lifelines have lower profile 6 volt batteries wich was usually the drawback to most using 6 volt. Our total amp hours is 720 giving us a "bank" of 360 ah to use. Our diet per day is about 120 with the alder barbar cold machine eating most of that at 3.5 amp per hour draw. This gives us three days with no alternative charging possibility. The agm accepts the charge quickly. The key to any battery bank as with anything is to do your maintainence and maintain the proper charging regimine. AGM requires less watching but are not maintainence free, The cost was high, but hopefully they will pay with their longevity. I recommend the Lifelines or the Trojan AGM. Even in a smaller bank two of the 6 volters pack a good punch. We also have an echo charger to our staring battery.

Dave

Dave
 

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The problem as I see it with AGM batteries (other than price) is that they have to be brought up to full charge every week or two. If you always tie up and use a shorepower charger no problem. But if you cruise extensively the engine can't take care of this. Solar or wind would be needed to get the last 15 or 20% of charge into them.
Brian
 

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Which is why I'm installing solar and wind. We intend to cruise in the tropics and the likelihood of a week of calm AND cloud is very low. We would typically haul anchor and go on a "pump out run" under power once a week or so anyway, but the goal is to have a week's worth of stored power without the necessity of firing up the diesel just to spin the alternator(s).

An advantage that is not generally considered to AGMs is that they don't leak electrolyte (acid). I have a steel boat. This is a plus to me. Battery acids leaks with "traditional" wet cells are rare (and the boxes are supposed to catch leaks) but if it's something I can avoid altogether, it's worth something to me.
 

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Discussion Starter #6
what is the maintenance required for wet cell battery besides charging?
 

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The DieHard battery above specs do not mention the amp hour capacity. I find that typical even in the deep cycle batteries. How do you compare them without that info. Can it be found anywhere else?

I found my own answer. The reserve capacity is the new supposedly better measure of battery capacity.
 

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David...reserve capacity is not the traditional 20 hour rate that works best for boaters and inter battery comparison.
Reserve capacity is the number of minutes you can run a 25 amp load which is pretty huge for sailboats and a more useful spec for cars.

20 hour capacity is the number of amp hours a battery can deliver over 20 hours at a fixed rate. i.e. a 100 ah 20 hr rating means 5 amps for 20 hours may be withdrawn.

The two specs are NOT directly related nor can one be calculated from the other as different plate thicknesses and construction details will make some batteries perform better at the reserve capacity rate...and others at the 20 hour rate.
The reserve capacity on the Sears battery above works out to 85 amp hours at a 25amp discharge rate. I would expect it to be around 100ah-110 ah at a 20 hour rate based on size and weight but cannot say with precision.

Saurav 16 ...if the battery you linked to is the one you have...it looks like those tabs with the warnings on them each cover 3 cell holes that need to be watered. There is no claim of a sealed battey in the description.
If what you have is truly a sealed WET cell...which are made for cars...that is a VERY bad choice for a boat on a dockside charger and I encourage you to return it and get a real fillable wet cell or a true sealed AGM.
 

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The DieHard battery above specs do not mention the amp hour capacity. I find that typical even in the deep cycle batteries. How do you compare them without that info. Can it be found anywhere else?

I found my own answer. The reserve capacity is the new supposedly better measure of battery capacity.
Right on the Sears page once you dig down, that battery specs out at 115Ah at the 20 hour rate. It actually looks like a good bang for the buck at $119
 
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