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Old 25-02-2012, 01:25   #1
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AGM vs Gel Batteries

Hi all,

I am considering changing my batteries this year. I have two, service and starter.

Now I need to know which type is best suitable for marine/my use ie what are the advantages or disadvantages of each type.

Or is one type better for the starter and the other for general/service use.

Consider that my batteries stay on the boat during winter layup, and that I have 10A shore power at my mooring.

What would you suggest?

TIA

Steve
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Old 25-02-2012, 01:35   #2
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Re: AGM vs Gel batteries

Steve, I would start by reading this article which might give you some different ideas:

Sterling Power Products: What is the best battery to use for an auxiliary charging system?

Personally I use good quality flooded lead acid batteries and get about 5 years from them before they need changing. Previous owner managed 7 but that is pushing it a bit. However, its probably the cost effective answer.

Just seen your in Germany, I found batteries very expensive and subject to a disposal tax when I lived there, are you planning any trips abroad were they may be cheaper?

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Old 25-02-2012, 01:47   #3
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Re: AGM vs Gel batteries

If you are looking for lots of amperage and storage, consider following home battery bank types,,they can be Gells or Agm but are usually combinations of six volts these types of battery banks are more suitable to repeated charge and discharge cycles.
The advantages of the Gell Cell are well know, so its down to personal choice i guess.
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Old 25-02-2012, 05:15   #4
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Re: AGM vs Gel batteries

gels cost more and you may need to change your entire charging system ie alternator regulator/battery charger as they will most likely overcharge them, id go with agms, which can usually directly replace lead acids with no modifications.
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Old 25-02-2012, 05:36   #5
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Re: AGM vs Gel batteries

just buy reasonable quality open flooded cells, expect to get 5-6 years. Unless you have extra-ordinary charging capacity or need a long standby period, then AGMs offer no advantage

GELS are extremely prone to overcharging and capacity loss and again, unless you need them to work when the boat is upside down, have no advantages on a boat.

Dave
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Old 25-02-2012, 05:42   #6
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Re: AGM vs Gel batteries

Quote:
Originally Posted by goboatingnow View Post
just buy reasonable quality open flooded cells, expect to get 5-6 years. Unless you have extra-ordinary charging capacity or need a long standby period, then AGMs offer no advantage

GELS are extremely prone to overcharging and capacity loss and again, unless you need them to work when the boat is upside down, have no advantages on a boat.

Dave
Talisker indicated he has a winter layover period which means AGM's would be better over flooded cells.
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Old 25-02-2012, 05:48   #7
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Re: AGM vs Gel batteries

you wont get 5-7 years out of lead acids if using all the time, if occasional use then maybe, only if very well looked after and good quality.

Agms have several advantages, they consume less energy to charge (ie lower internal resistance) and loose less to internal resistance when discharging, they can be stored on their sides, dont leak. they can usually be cycyled more than flooded cells. You can charge them much faster saving generator run time.

Though for occasional use ie not on the hook for long periods then they don't offer much advantage.
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Old 25-02-2012, 06:08   #8
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Re: AGM vs Gel batteries

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Originally Posted by stevensuf View Post
you wont get 5-7 years out of lead acids if using all the time, if occasional use then maybe, only if very well looked after and good quality.

Agms have several advantages, they consume less energy to charge (ie lower internal resistance) and loose less to internal resistance when discharging, they can be stored on their sides, dont leak. they can usually be cycyled more than flooded cells. You can charge them much faster saving generator run time.

Though for occasional use ie not on the hook for long periods then they don't offer much advantage.

Stevensuf, Lets looks at AGMs carefully

(a) Less energy to charge

Well this is a red herring, Gains are a small proportion of the losses inherent in the charging system. In effect such efficiencies have little overall effect.

(b) Loose less internal resistance when charging,

Somewhat a confused electrical comment, but I take it to mean lower internal resistance when charging, i.e. higher acceptance rates.

However this is if little advantage unless you have a large capacity ( read expensive) charging system. Most boaters don't have that.

If you mean that they have a low self discharge, yes thats true, but thats of little use to boaters


(c) stored on their side

Your boat spends a lot of time at 90 degrees !!!!!


(d) Cycled More, no evidence of that from the specs.


(e) faster charging less generator time, only if you have the high capacity charging system and the proper controls to do so.


AGMs were developed for fighter jets, primarily to prevent leakage when shot at!. They have great characteristics for people that needs theses characteristics. Most boaters do not. Hence they are a incorrectly specified part on a boat. This is a function of nonsense marketing, whereas inappropriate advantages are impressed upon buyers, that are impressed by such claims.


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Old 25-02-2012, 06:16   #9
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Re: AGM vs Gel batteries

As a previous poster noted, it depends a lot on your use and charging system. I have lead acid for the start and dc system on the boat, maintain the levels and they are in their 6th year. These are the 6 volt Golf cart type. The house bank which is only used to supply the ac inverter system are two expensive gel type 8D's made in Germany. These are charged only through the inverter charger which is controlled by the Links 2000. They are 12 years old and in perfect condition. The secret to their long life is controlled voltage charging. They can take a high current input but not a high voltage input. The number of AGMs I see being changed at our dock leads me to believe that they are not worth the expense. I guess they are ok if you don't like doing monthly battery checks and top ups.
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Old 25-02-2012, 06:18   #10
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Re: AGM vs Gel batteries

dave.
Actually check up on the energy lost while charging it can be as high as ten percent, to me charging by solar ten percent is a huge number!

Batteries have what is correctly known as "internal resistance" this is what limits how much current can come in or go out" the heat generated in the batteries as they charge or discharge is the direct result of this internal resistance.

In flooded batteries, say a starter battery , it has more thinner plates, to allow a lower internal resistance providing more current, a leisure battery has fewer thicker plates, which reduces how much current they can supply due to a higher internal resistance (ie smaller surface area) thicker plates are less prone to sulfation than thinner plates, hence deep cycle batteries have lower current capacity.

Agms due to their construction nature have superior deep cycling capacity yet again.

Steven (bsc hons electrical engineering)
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Old 25-02-2012, 06:19   #11
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Re: AGM vs Gel batteries

And yes i have seen acid leak out of batteries from a well heeled yacht!
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Old 25-02-2012, 06:20   #12
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Re: AGM vs Gel batteries

With proper maintaince, Ive almost always gotten 5-6 yrs out of my lead-acid batts. I admit Im a little anal about checking my batts daily,watching levels, heat ect, and makeing sure proper charging levels are maintained. but Im retired on a pretty much stable, but moderate income LOL so I make things last as long as I can within safe guidelines. Just my 2 cents Bob and Connie and PS Ive mostly had deep keel boats and don't worry about turning over LOL
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Old 25-02-2012, 06:30   #13
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Re: AGM vs Gel batteries

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Originally Posted by stevensuf View Post
Agms due to their construction nature have superior deep cycling capacity yet again.

Steven (bsc hons electrical engineering)
Okay, so what is the cost effective answer?

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Old 25-02-2012, 06:38   #14
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Re: AGM vs Gel batteries

well i did recommended flooded for the original posters use, i never said agms were the best for the op, they certainly are a better choice than gels for his use as the original post was gel vs agm, but is day for his use flooded are the cheapest and best all round for occasional use, if the batteries are to be used heavily with some abuse then agms will be more cost effective and a better choice
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Old 25-02-2012, 06:47   #15
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Re: AGM vs Gel batteries

here is a very good study of batteries for marine use , he even works out cost vs life per watt a bit anal, but there you go!
Battery Types: Flooded versus AGM and Gel
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