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saurav16 07-28-2009 04:52 PM

Marine Battery Weigh in

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!

camaraderie 07-28-2009 08:55 PM, 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.

chef2sail 07-29-2009 12:00 AM

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.



mitiempo 07-29-2009 12:37 PM

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.

Valiente 07-29-2009 01:22 PM

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.

saurav16 07-30-2009 09:16 AM

what is the maintenance required for wet cell battery besides charging?

scottyt 07-30-2009 01:36 PM


Originally Posted by saurav16 (Post 509719)
what is the maintenance required for wet cell battery besides charging?

topping with or at least checking the water monthly. more often if you over charge, do a real deep charge, or use them heavy

camaraderie 07-30-2009 02:53 PM

-Add equalization every 60-90 days to scotty's list.
-Monitor battery use with a battey monitor when you are aboard and using them and never go more than 60% capacity discharge...keep it to 50% if possible. (This last applies to AGM/Gels as well)

saurav16 07-30-2009 07:21 PM

I thought my battery was sealed like a car battery and you didn't need to add water. Still using the previous owners batter:

DieHard Marine Deep Cycle/RV Battery, Group Size 29HM

Is it sealed/maint. free, like a car battery?

davidpm 07-30-2009 10:43 PM

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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