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Discussion Starter · #1 ·
Does anyone know the difference between an dual-purpose AGM battery verses a deep cycle? I found what I think is a good sale this weekend on Seavolt dual-purpose AGM batteries but don't know if it's really a good deal.
 

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Most likely the dual purpose is a deep cycle. The dual purpose means you can use it for starting and basic electrical. Most sailboats run their house bank as a starting bank too - especially in the smaller boats.

Just get the "dual purpose". What size is it?

And just a note, explained to the best of my knowledge, is that a "starting" battery is different from a deep cycle battery in design. It has to do with the plates which, on a deep cycle, are thicker and can give more ah but also require a different charging regime to replenish the plates since you have to replenish the 'inside' of the plates versus a thin exterior. The flip side is the starting battery which has thin plates meant for a quick (high amp) burst, quick discharge, and quick recharge. However, again to the best of my knowledge, there is not a set government stadard for what thickness plates have to be to be a 'starting battery' versus 'deep cycle' versus 'dual purpose'. I think it all depends on the original design focus, how reputatable the manufacturer is, and how creative their marketing team is.

My opinions.

- CD
 

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Discussion Starter · #3 ·
The battery is a Seavolt AGM Group 24 AH -79 MCA-735 on sale this weekend for $149.99 at West Marine.
 

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I'm not saying I wouldn't use this battery under any circumstances, but I will quibble a bit with CD about whether this is a good battery for your purposes.

I assume you are looking to use this for a "house bank" battery? If so, I would go with a true deep cycle.

My understanding is that the dual-purpose batteries are not true deep cycles, but a reasonable compromise between a starting battery (like the one in your car) and a deep cycle. As such, they are primarily intended for motor boats, where there are many more start/stops of the engine, and lots of available charging to top them off (because they do not have the same ability to be "drawn down" like a true deep cycle).

Sailboats have a very different use profile than a motor boat. In a sailboat, I would only consider a dual-purpose battery if I was going to install a dedicated starting battery. For a straight "house bank" I would want true deep cycle batteries (whether they be AGM, gel, wet-cells).

Don't worry if you don't have a dedicated starting battery -- standard deep cycle batteries can manage a sailboat's starting loads just fine.
 

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Discussion Starter · #5 ·
So basically the wrong battery at the right price is still the wrong battery:laugher I already have one of these batteries for bank one but need to replace the other two in bank two. They don't hold a charge as good as they did in the past but this is a 20 yr old Cat30 and the batteries are 7 years old. The battery from bank one had the + post corrode right off of it so I replaced it with a dual purpose. My plan is bank one for starting and bank two for the house. I do need to figure out what is crossed up because when I "unplug" all but one battery, the gauge on the panel shows good voltage switched to either bank one or two. Another day of fun on this old boat .
 

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I have a pair of Seavolt 6Vs lead-acid ganged together as the house bank for my boat. They're fine but they aren't nearly as good as the 18 year old Trojan T-105s I pulled out of there in 2006. Yes, 18 years of Canadian winters and no record of service and they could still turn over the diesel...they just couldn't hold a full charge anymore.

To my knowledge, Deka/East Penn do a lot of the "house brand" batteries. Frequently a good test is to check out their website and look at the equivalent Deka/East Penn model. Often they are identical to the WM house brand, save for the colour of the plastic and the label on the top.

I just got off the phone with a buddy who has two East Penn 8D AGMs with which he is very happy. He noted how well they held their charge compared with lead/acid over our Toronto winter. Whether that's important to you is moot.

I'm likely going to 8D AGMs for world cruising shortly, but the brand is still up in the air. I like Lifeline and Discover brands so far.
 

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Val...Consider the Odysseys. I would go with them if I were starting from scratch and I think you will have the capabiity of taking advantage of their qualities of very fast charge and deeper discharge % levels.

I agree the T105's are better than the seavolt lead-acid or most standard lead acids. I like the Deka AGM's and I think they are as good as the Lifelines at a lower price...but I think the Odyssey is worth the premium IF you can take advantage of them since they will pay for themselves.
 

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I'm a little worried about the durability of the thin lead mesh in the Odysseys standing up to the "dynamic" environment of a sea-going boat. Part of my hesitation is concern about the durability of this relatively new battery type and manufacturing process, and the other is about the duty cycle. Unlike most coastal cruisers, my situation is such that I don't need smallish battery banks that can be charged quickly and can be drawn down to 50% without harm. I don't even need the aspect of a battery that will hold its charge after a month idle. I have the space, and soon, the means to have a really big bank (4 x 8D) with multiple charge sources (4 x 135W solar; Air-X wind genny; Honda 2000; two 75 amp alternators) and a relatively modest draw (fridge, radar, plotter, a bunch of LED lights...meh...).

So I'm focused on the "brute force" aspects and certainly on durability and ease of replacement. I'm like the guy who just wants "a car"...not a 2009 Ford Fabuloso with DVD/hologram and 22 coffee cup holders and a seat that shouts out directions en espanol...
 

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Try to stick to a starting battery high current capability and deep cycle battery for house if you can afford 2 banks. I installed AGM's 5 yrs ago and swear by them. Only concern is charging them. Improper charging will reduce their life as most batteries, more forgiving than the old gel cells. They have a higher acceptance level for quicker charging than wet cells and can take the discharge cycles better. Remember the deeper the cycles the less cycles there will be. AGM's were originally designed for military durability in aircraft. Nice to have them for reliability in the boat.
 

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Val...I guess the Odysseys don't have much advantage for you over standard AGM's since you are likely t replenish your amphours in slow mode on a 24 hr. basis. They are a great solution for those who want to cut down on engine or gen run time for charging...and for those who need a bigger bank but don't have the room.
I don't think there is anything lacking in their actual construction given the applications they were originally designed for and the details available on their site. I've not heard reports of any failures in a couple of years on the market.
Sounds like going the standard AGM route is the right choice for you.
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Roline- no argument on the advantages for AGM house bank...but to be clear...the starter should also be agm as the charging parameters for wet and AGM are different and types should not be mixed in the same charging system which MUST be a 3 stage system...including from the alternator/regulator.
BTW...I am referring to "cruising mode" here. If you keep your batteries topped up with a 3 stage charger at the dock and only go out weekends...the AGM's will last just fine without changing out the alternator/regulator system.
 

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The Seavolt is really a Deka y East Penn AGM and it is a deep cycle battery despite the dual use advertising by West. Go get your deal.
Ahh, it's the old "give them more for their money" trick.:D Thanks for clarifying that.


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BTW...I am referring to "cruising mode" here. If you keep your batteries topped up with a 3 stage charger at the dock and only go out weekends...the AGM's will last just fine without changing out the alternator/regulator system.
That's pretty much our use/charge profile (though we're on a mooring so the 3-stage charging is for 4 winter months continuous and only intermittently throughout the sailing season.) I can't remember whether I installed those Lifeline's in 2003 or 2004, but they're still going strong. Zero maintenance. No complaints. Touch wood.;)
 

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That's pretty much our use/charge profile (though we're on a mooring so the 3-stage charging is for 4 winter months continuous and only intermittently throughout the sailing season.) I can't remember whether I installed those Lifeline's in 2003 or 2004, but they're still going strong. Zero maintenance. No complaints. Touch wood.;)
Yeah John...same basic profile and the AGM's work particularly well on a mooring since they don't lose charge much just sitting there.
Would probably help extend the life if you draw the batteries down to 40-50% a few times during season and then pull into a marina for a recharge.
I believe you can also EQ the Lifelines when you start to notice some loss of capacity.
 

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Yeah John...same basic profile and the AGM's work particularly well on a mooring since they don't lose charge much just sitting there.
Would probably help extend the life if you draw the batteries down to 40-50% a few times during season and then pull into a marina for a recharge.
I believe you can also EQ the Lifelines when you start to notice some loss of capacity.
Yes, being on a mooring, the slow-discharge rate (along with the no/low maintenance and faster acceptance rate) was what originally drew us to the AGMs eight or nine years ago (we installed them on our Dana, too, along with a Balmar alternator and MC612 regulator).

I think our normal use pattern draws them down pretty well, especially our several 5-10 day trips per season (refrigerator). These almost always include a couple nights at a marina plugged into shore power.

But I didn't know there was an "equalization" protocol for these batteries. I will need to study up on that, and review the manual for our Statpower Truecharge 20 unit. I think I recall that while hooked up for the winter months the charger cycles them through all the charging stages about every 3-4 weeks.

Thanks!
 

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Ok, you guys lost me. Ive been following this thread with great interest because the WM sale ends 5/31 and I need at least one new battery.
presently I have two five year old wet cell/dual cycle battey that I use for both starting and house My boat is on a mooring and the only chargeing comes for the alternator.
If I replace one of the wet cells with an AGM do I have to change he charging curcuit.. BTW I'm on the boat around 20 hours/week and have the egine running maybe 20% of that time.

next year I'll be at a dock with a shore power hook-up and a "real" charging curcuit.

John
 

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Your batteries should be either both lead/acid or both agm as they require different charging regimens.
Brian
 

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Ok, you guys lost me. Ive been following this thread with great interest because the WM sale ends 5/31 and I need at least one new battery.
presently I have two five year old wet cell/dual cycle battey that I use for both starting and house My boat is on a mooring and the only chargeing comes for the alternator.
If I replace one of the wet cells with an AGM do I have to change he charging curcuit.. BTW I'm on the boat around 20 hours/week and have the egine running maybe 20% of that time.

next year I'll be at a dock with a shore power hook-up and a "real" charging curcuit.

John
If I were in your position, I would change a lot of things. However, if you are charging off the alternator, is it a 3-stage or does it just pump straight 14.2? If the latter, I probably would not invest in AGM's. On one side, you will benefit from the low power loss (less than 1% IIRC). On the other side, they will never get fully charged and you will realize a short lifespan. Given that, I would go with the cheapest battery I could.

Have you looked at Sams? They sell wets. The last one I saw was an 8D. Seems like it was $150-$200. Could you fit that or a 4-D or even some smaller batts? Just a thoought. If not, check with Interstate or some of the other mfg's and don't waste your money with West.

My opinions,

Brian
 

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Ok, Given that I will upgrade my charging system next year (another research project) will I wreck a agm using it with my system for one year?
I'll find out tommorow if my alternator is a multi stage.

If so then it's off to BJ's to see what they have for marine deep cycle wetcells

John
 

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NO battery will do well without optimum charging. Some are more tolerant than others. That is why I suggest going the cheapest route and overhauling your system when you are plugged into the dock for sure. Until then, a wet cell will get you by.

My opinions.

Brian

PS Your alternator will generally be run into a controlling board or regulator (for lack of a better name) which sets the voltage for 3 stage. Go here: page14-Regulatorsmain

Balmar pretty much has the market in this area, though there is a lot of conjecture on how good they really are. This is for instructional use only.
 
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