Deep Cycle AGM Batteries

[seahouse]

Hey HaminX!

Something’s mixed up there.

As you have correctly pointed out, both AGM and flooded-cell conventional deep cycle batteries use the same lead-acid chemistry, they differ in their construction.

Since the chemistries are essentially identical, under identical usage patterns AGM batteries will not last “twice as many seasons, thus saving money”. Not even close.

I have a backup photovoltaic battery bank for my house. It, like virtually all such PV configurations worldwide, including most commercial installations, use deep-cycle flooded-cell lead-acid batteries. For good reason. Nothing has beat them in the last 100 years. Not yet.

I’m not so inclined to beleaguer the point, but to use cost savings, or even break-even points as a rationale for using (new) AGM batteries is not a fact-based course that I would advise anyone to take.

Hey yukonbob!

Yah, Costco, I’m a big fan. They vet their products so thoroughly I’m sure it’ll be of good quality too.

Their AA batteries consistently outperform others on the market, including (unbelievably, I know) their manufacturer’s own brand labeled batteries. Yes, you read that correctly, somebody manufactures (or did in recent years, it’s been a while since I saw it, hope they keep it up) batteries for Kirkland to a higher standard than their own. And cheaper too. (Consumer Reports)

Hey Bartmac! – Used ones; the ultimate in recycling, I love that idea!

Rgds- Brian.

[yukonbob]

Hey yukonbob!

Yah, Costco, I’m a big fan. They vet their products so thoroughly I’m sure it’ll be of good quality too.

I should clarify that they are brand name optima 34 blue tops for 114 ea not cosco brand.

[seahouse]

Bob -

I should clarify that they are brand name optima 34 blue tops for 114 ea not cosco brand.

Yah - and I was meaning that they vet all brands they carry.

- B.

[Hamin' X]

Under deep discharge use, flooded cells suffer from sulfation much more severely that AGM cells. Sulfation is a precipitant that forms in the electrolyte and settles to the bottom of the case, shorting out the plates and killing the cell. there is no free electrolyte in an AGM for this precipitant to settle from. Under deep discharge conditions, AGM cells will have more cycles than flooded.

~Rich

[seahouse]

Hey Cat!

At West Marine a group 24 AGM sells today at 215 USD - I can get a Group 24 deep cycle battery for about 90 USD, so the capital cost advantage is about 2x ish for the flooded cell type. Lifetime of the battery will obviously depend heavily on usage patterns etc, so each boater has to make this call individually - there is no 'right answer' on the cost issue.
Ive replaced my flooded cell Group 24 once since 2002 - and that was more because I let them sit discharged one winter.

You do not need a starter battery with the outboards on Macs - especially with an EFI engine, where crank time is minimal.

Are you going to make me do your homework? ... ... ... Again!!! (Written facetiously, of course).

Using your figures- an AGM will have to last more than twice as long just to break even. Very true, but, under identical conditions, they don’t come any where even close, and sometimes less under some circumstances, as RobertB has witnessed first-hand.

And that’s without substituting XD-100 for acid. (Facetious, again)!

Ditto on using a deep cycle batt for starting a modern outboard, no upsize needed for any motor that you will find on our boats.

Cheers! -Brian.

[seahouse]

Hey Rich!

Under deep discharge use, flooded cells suffer from sulfation much more severely that AGM cells. Sulfation is a precipitant that forms in the electrolyte and settles to the bottom of the case, shorting out the plates and killing the cell. there is no free electrolyte in an AGM for this precipitant to settle from. Under deep discharge conditions, AGM cells will have more cycles than flooded.

~Rich

Interesting. Haven't seen that before about AGM's. Sulfation happens on the surface of the plates. Any reference for that giving such a marked improvement in lifespan?

Twice as much (it would have to be more than twice, really) is a considerable amount to make such a difference.

- Brian.

[yukonbob]

Bob -

I should clarify that they are brand name optima 34 blue tops for 114 ea not cosco brand.


Yah - and I was meaning that they vet all brands they carry.

- B.

Ahh gotcha

As for cca on deep cycle batts. This may be the case for most but had issues this spring in the cold mornings trying to start when the oil is like molasses. Had to lighten the oil until it get warmer Killed the dedicated starter twice trying to start.

[NiceAft]

I purchased two AGM batteries from Cabelas last year. I did not have any problems with the posts.


If I remember correctly (getting old. minds going), these batteries are tall. In order to fit them into the battery compartment in my , I had to remove the companion way stairs. That was quite a job. The stairs support the cockpit floor. When I went to reinstall the stairs, they would not fit into place. I had to jack up the cockpit floor from below in order to align the bolt holes.

I purchased a larger battery than you indicate, so the difference in height may make all the difference in the installation.

Ray

PS. Here is a link to the postings that ensued when I encountered the problem. http://macgregorsailors.com/forum/viewt ... 99#p214999
Again, a shorter battery may make the difference.

[DaveB]

I agree, just don't let your deep cycle batteries go below 50% discharge and charge them as soon as possible so they won't sulfate.
The big Question is to spend the money for a AGM battery that last 5 years or a wet cell deep cycle that last 3 years .
Deep Cycle 29 group wet cell $80. AGM group 29 group closed wet cell $ 190.
If you don't ck your wet cell batteries every 2 mo. or so( I haven't added water in 6 mo. on my twin 29 deep cycle batteries ,Wall-Mart) I would go with the AGM and don't worry about cost.
Same thing if you wanted to go with twin 6 volt golf batteries , at $75 each.(Golf batteries will last a long time when used as house and twins. Just as much as a AGM but they still need fluid.
Important thing to remember: if you run down your House batteries to 50% often than you need to ck the water level often.
If you top them off and don't go below 50% than a deep cycle wet cell battery should last you 5 years or more.
I have had twin Gell house Batteries on my Potter, Twin Golf 6 volt batteries on my Compac19, and now twin 29 wet deep cycle on the Mac. (All house batteries)
I won't tell you how the Die Hard deep cycles worked on my 35 ft'er to the Carribean. I will just say they Died very quickly and hard.
Dave

Under deep discharge use, flooded cells suffer from sulfation much more severely that AGM cells. Sulfation is a precipitant that forms in the electrolyte and settles to the bottom of the case, shorting out the plates and killing the cell. there is no free electrolyte in an AGM for this precipitant to settle from. Under deep discharge conditions,

~Rich

[WASP18]

http://batterytender.com/#sf
Here's a "Deltran Battery Tender" I've been using on our family cars (GMC Savana Explorer conversion, Honda Accord, Ford Escort) with success. I charge the batteries in September or October every year and we sail through the New England winters without any hint of battery weakness. The batteries are charged very slowly (24 hours for the van) up to a maximum charge. The charger then shifts into a microprocessor controlled float mode. This gadget is great for seasonal toys like motorcycles and boats. You can leave it attached throughout the winter without worrying about overcharging. Costs about $42 at Amazon.

[tek]

This has been an informative thread as I had been putting some serious thought into replacing the house batteries on my .

The cost isn't so much a factor for me as safety, since the AGM's won't spill if inverted or cracked, and don't vent hydrogen.

This is one area our macs fell short from the factory. There is no battery box to contain gases or spills, and there's no vent run to vent the hydrogen outside.

I had considered upgrading by constructing a battery box and vent, but have decided swapping to AGM's might be the better move. The cost shouldn't be significantly different between the 2 options, and I don't have to put another hole in the boat somewhere for a vent line.

I've noticed both the 24, 27, and 29 size batteries mentioned, does anyone know what the largest type of battery is for which you can fit two side by side in the batter compartment of an ?

[seahouse]

Hey Rich!


Under deep discharge use, flooded cells suffer from sulfation much more severely that AGM cells. Sulfation is a precipitant that forms in the electrolyte and settles to the bottom of the case, shorting out the plates and killing the cell. there is no free electrolyte in an AGM for this precipitant to settle from. Under deep discharge conditions, AGM cells will have more cycles than flooded.

~Rich

Interesting. Haven't seen that before about AGM's. Sulfation happens on the surface of the plates. Any reference for that giving such a marked improvement in lifespan?

Twice as much (it would have to be more than twice, really) is a considerable amount to make such a difference.

Hey Rich - any reference for that? Did you just make that up?
- Brian

[Hamin' X]

Actually, I misstated part of it, as the "precipitate" that falls to the bottom is really particulate matter that flakes from the plates of regular flooded cell batteries. It is cause by the sulfation of the plates getting into the spongy lead that the use to try and increase capacity and reduce inter cell resistance. This same construction reduces mechanical strength. As far as the number of cycles with an AGM cell, that is common knowledge and available from many sources.

~Rich

[seahouse]

Thanks Rich - can you point me to one?

[WASP18]

I ran a test on one of my new 75 amp AGM batteries inside my home. I first charged it to 100% because most new batteries are not fully charged. I then attached a small inverter (600 to 800 watts max) to the battery and plugged a DVD player and three speakers to the inverter. The player and speakers plug in separately. I played a two hour movie (it was a rainy day) and then checked the battery voltage. From a starting point of 14 volts, the battery dropped to 13 volts. I recharged the battery using the slow charge option of 2 amps. The recharging took three hours. I'm sure the charging time would have been faster using the "normal" charge setting but I understand that a slow charge is longer lasting and more effective.