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Old 30-07-2017, 18:11   #1
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AGM or Wet Cell

Hi, We have just bought our first cruising yacht and will be living aboard soon. We need to replace its house batteries and I am tossing up between a Wet Cell versus AGM Trojan Batteries. The Marine electricians recommend AGM however we have heard that Wet Cell are still offer the best results for live aboard cruisers. Can anyone offer us their thoughts.
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Old 30-07-2017, 19:25   #2
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Re: AGM or Wet Cell

FLA are very robust, generally last longer,

Best advantage besides lower cost, is getting very accurate SoC data from a cheap hydrometer, even if only to properly calibrate your SoC monitor.

Main disadvantage is usually a lower CAR, but that is important in only niche use cases.

Personally the only compelling reason to go AGM is the install space requires going sideways or prevents access to the caps.
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Old 30-07-2017, 20:15   #3
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Re: AGM or Wet Cell

If your not going to be living aboard in a Marina, you don't want AGM.
If money is even partially an object, you don't want AGM.
Reason I have AGM is they are shorter and FLA won't fit into my box, it would have been a major job to modify it, and even then I may not have room, the bottom of the box is awfully close to the hull
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Old 30-07-2017, 20:48   #4
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Re: AGM or Wet Cell

The marine electrician should be able to give you the best advice since they would know the boat and would have extensively discussed how you would be using it. Of course, they could just be trying to sell you more expensive batteries...

I really like FLA (flooded lead acid) or wet cells. For most applications, I think they are still the best value. Having said that, I just replaced my old SLA (sealed lead acid) batteries with AGM. They happened to best fit my needs.


I would look at wet cells if:
-you have good access to your batteries so you can regularly check the water
-you don't have a specific need to be able to recharge your batteries as quickly as possible.
-you don't need to put your batteries in a space where off-gassing would be a problem
-the batteries will be upright.


If not, look at AGM. In either case, you will be well served by learning as much as you can about the care and feeding of batteries. I suggest going to www.marinehowto.com and read everything that RC Collins has on that site about batteries and charging.

BTW, congratulations on the new boat.
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Old 31-07-2017, 03:01   #5
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Re: AGM or Wet Cell

Thanks guys.

Everyone seems to support my conspiracy theory that AGM is recommended due to the lower risks and higher profit not for their performance.

We do plan to cruise outside of marinas swinging on the hook and have two interconnecting areas that is capable of storing 6 to 8 FLA batteries. I found out that the previous owner had cooked his set of 6 FLA batteries (I believe the solar regulator needs replacing) and replaced them with 3 brand new AGM's which have failed in 3 months (I believe once again due to the solar regulator)

So I was apprehensive when the marine sparky recommended AGM's again.

Is off gassing anything worth considering? or is this just further evidence of my conspiracy theory.

And thanks dhays, its exciting times! Got the yacht ... now we are selling the house!
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Old 31-07-2017, 03:08   #6
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Re: AGM or Wet Cell

Even mistreating my Trojan wet cell battery bank for the first four years, they still seem to be going strong after five years and now into the middle of our sixth cruising season.
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Old 31-07-2017, 03:09   #7
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Re: AGM or Wet Cell

Quote:
Originally Posted by Higgo View Post
Thanks guys.

Everyone seems to support my conspiracy theory that AGM is recommended due to the lower risks and higher profit not for their performance.

We do plan to cruise outside of marinas swinging on the hook and have two interconnecting areas that is capable of storing 6 to 8 FLA batteries. I found out that the previous owner had cooked his set of 6 FLA batteries (I believe the solar regulator needs replacing) and replaced them with 3 brand new AGM's which have failed in 3 months (I believe once again due to the solar regulator)

So I was apprehensive when the marine sparky recommended AGM's again.

Is off gassing anything worth considering? or is this just further evidence of my conspiracy theory.

And thanks dhays, its exciting times! Got the yacht ... now we are selling the house!

Best price/performance ratio BY FAR for lead-acid batteries is Costco 6v golf cart batteries. These are bulletproof (made by Trojan I believe), cheap, very long lasting.

Bit of a PITA to keep flooded batteries watered, and you can't mount them on their sides, but otherwise AGMs don't offer any practical advantages at all and are far less cost effective, and don't last as long. They have higher charge acceptance rates, but the charge acceptance rate of a large flooded bank is going to be beyond the capacity of your charging sources anyway, so you don't care.


The future is with lithium technologies, however. Many (including me) think they are not quite ready for prime time except for the adventurous, but my next batteries will probably be LiFePo's.
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Old 31-07-2017, 03:09   #8
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Re: AGM or Wet Cell

I had both problems. Out gassing was causing corrosion problems and one of my batteries was difficult to get to.

I replaced all the FLA batteries with Gel. It's been almost a year, with half of that on the hook, and so far, so good.
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Old 31-07-2017, 03:48   #9
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Re: AGM or Wet Cell

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Originally Posted by a64pilot View Post
Reason I have AGM is they are shorter and FLA won't fit into my box, it would have been a major job to modify it, and even then I may not have room, the bottom of the box is awfully close to the hull

I'd suspect that's a less common factoid, and that AGMs in general are not by definition shorter than FLAs. I've seen where manufacturers have been a bit adventurous with standard BCI Group dimensions, but didn't see a pattern.

-Chris
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Old 31-07-2017, 03:57   #10
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Re: AGM or Wet Cell

Quote:
Originally Posted by Higgo View Post
Everyone seems to support my conspiracy theory that AGM is recommended due to the lower risks and higher profit not for their performance.

Is off gassing anything worth considering? or is this just further evidence of my conspiracy theory.

I think off-gassing can be a consideration for some, but maybe/maybe not for you. Might depend on where your batteries are located relative to living space, or systems where continuous exposure to acidic gas wouldn't be great.

FWIW, we've had/we're having good luck with AGMs, possibly at lower cost than FLAs would have been. Choice was mostly driven by access issues, and our first sets did indeed cost more than most FLAs... but then the oldest bank lasted about 11˝ years, maintenance-free, no muss, no fuss... so we got our money's worth, in both direct cost comparison and certainly when considering my maintenance time (zero, i.e., lack thereof).

Our circumstances are such that we're able to fully recharge often, though, and that seems to be a serious consideration with AGMs.

-Chris
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Old 31-07-2017, 04:37   #11
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Re: AGM or Wet Cell

According to my research on the issue.

AGM

Pros
- Can take higher bulk charge BUT you must have that capacity in your charging system and the total time to reach 100% SoC (state of charge) is only slightly better than a standard FLA
- Maintenance free.
- Can mount in any orientation

Cons
- expensive
- needs to be fully charged on a regular basis to avoid early death
- Can die and early death if proper charge regime not followed. This of course can happen to any batteries but AGMs in general are more susceptible and the loss much more that killing off a set of FLAs.

FLA

Pros
- Generally the most robust, easy care, (except need to add water unless special caps are added), tolerant of abuse type battery.
- Tolerate partial charging better than most batteries.
- Most bang for the buck.
- Readily available almost anywhere.

Cons
- Generally require some maintenance
- Can only mount upright
- self discharge and can die if left untended for long periods.
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Old 31-07-2017, 04:55   #12
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Re: AGM or Wet Cell

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Originally Posted by Dockhead View Post
Bit of a PITA to keep flooded batteries watered...
This is not really a problem since there are watering systems where you replace the standard FLA battery plugs with the special ones that include a valve and water connections.

Watering of my battery bank takes less than two minutes and that includes taking out the pressurized distilled water tank (a 5l garden spry) from it's storage.

P.S. Lithiums are ready. Just too dear for most of us.
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Old 31-07-2017, 05:10   #13
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Re: AGM or Wet Cell

I can see the common thread of the cost benefits and durability of the FLA's, however the maintenance free benefits of AGM can't be ignored.

The batteries will be located in the underneath the saloon area seating

In relation to recharging we do have 4 x 140watt and 2 x 85watt solar panels. Would these solar panels supply enough power to regularly recharge the AGM's to 100% SoC. Our aim is to use the gen set as little as possible.
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Old 31-07-2017, 05:40   #14
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Re: AGM or Wet Cell

Depends on the latitude and weather of course, and positioning, preventing shading.

I like a 2:1 ratio, so 700w roughly covers 350AH.

Get a good SoC monitor and do what it takes to get to 100% Full most cycles.

If you need to run the genny, do it in the morning, and that justifies a high-CAR AGM to reduce runtimes.
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Old 31-07-2017, 06:19   #15
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Re: AGM or Wet Cell

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