Flooded VS. AGM Pros and Cons

I am currently running Scorpion AGM batteries in all my vehicles,motorcycles,and L&G equipment.I love these batteries because they haven't died from vibration or inactivity.However,I have never used them in a boat or RV.I have no experience with them over a long period of time.What I am trying to do is find the pros and cons to justify the expense of going with all AGM batteries instead of flooded.

My system will consist of three "banks".
Starting-1 12V
Bow battery-1 12V-this is for the windlass,wash down pump,and possibly a small bow thruster.
House-4 6V wired for 12V to inverter

Without posting all the math and variables,I averaged a cost of $8-1000 for flooded and $2-2500 for AGM.I have ran a lot of flooded Trojan batteries in electrical equipment over the years, so I am very familiar with the up keep of flooded batteries.I have the equipment on hand to deal with them.

FLOODED
The down side of flooded is the up keep and venting required to keep the batteries happy.I also hate when they boil over and make a mess.This also limits where the batteries can be located in the hull.

The upside is I know how to keep the batteries happy which will negate most of the mess of boil overs.They are roughly 1/3 the cost of AGM.


AGM
The down side,cost.

The upside,less up keep and they can be placed anywhere without much worry.


Since the boat will be trailered to cruising grounds for a couple years, before doing the great loop.I may go with flooded and replace them with AGM as they go bad.I know AGM and flooded can't be mixed on the house bank.So no need to point this one out.

So what's the pros and cons that I am not think of?Why AGM?

Other than up front cost, there are no "cons" to AGM batteries for marine use. A lot of folks (including me) feel that the Sears Die Hard Platinum Marine group 31 AGM is the best without dealing with costly specialty batteries.

If you are building a boat, the additional cost of AGM batteries will be insignificant compared to the cost of the boat.

They have flooded battereis now days that are "sealed" in a limit fashion. No way to add water, and in theory, no need to. Since my start bank is almost impossible to get to I have a pair and will see how they work. Sam's sells them among others. My battery charger won't handle a mixture of batteries so I went cheap with the flooded batteries. Don't have a big load since we don't live aboard or camp, but I do have two 6 volts in series that do have covers that I can get off to service. They are easier to get to.

ben2go said:

I am currently running Scorpion AGM batteries in all my vehicles,motorcycles,and L&G equipment.I love these batteries because they haven't died from vibration or inactivity.However,I have never used them in a boat or RV.I have no experience with them over a long period of time.What I am trying to do is find the pros and cons to justify the expense of going with all AGM batteries instead of flooded.

My system will consist of three "banks".
Starting-1 12V
Bow battery-1 12V-this is for the windlass,wash down pump,and possibly a small bow thruster.
House-4 6V wired for 12V to inverter

Without posting all the math and variables,I averaged a cost of $8-1000 for flooded and $2-2500 for AGM.I have ran a lot of flooded Trojan batteries in electrical equipment over the years, so I am very familiar with the up keep of flooded batteries.I have the equipment on hand to deal with them.

FLOODED
The down side of flooded is the up keep and venting required to keep the batteries happy.I also hate when they boil over and make a mess.This also limits where the batteries can be located in the hull.

The upside is I know how to keep the batteries happy which will negate most of the mess of boil overs.They are roughly 1/3 the cost of AGM.


AGM
The down side,cost.

The upside,less up keep and they can be placed anywhere without much worry.


Since the boat will be trailered to cruising grounds for a couple years, before doing the great loop.I may go with flooded and replace them with AGM as they go bad.I know AGM and flooded can't be mixed on the house bank.So no need to point this one out.

So what's the pros and cons that I am not think of?Why AGM?

Click to expand...

One advantage of AGMs that tipped me in that direction is their superior absorption rate. You can have all the charging capacity in the world, but if the batteries won't soak up the current you still spend a long time charging. Perhaps the higher cost is offset somewhat by less charging time than flooded.

We are beginning our 8th season with a set of Excide Orbital AGM batteries. One starting battery and two house batteries, all three manufactured in August of 2004.

We love the fact there is no unabsorbed acid. Absolutely no corrosion to battery terminals. No charging odor. No chance of spillage or leak or ruined battery trays.

AGM's don't self discharge as rapidly as flooded batteries so they don't self distruct from sitting discharged as quickly.

Great to know they absorb charge faster than flooded. I'm a convert.

I can speak to longevity, the two 8d AGM's on my last boats thruster are over 8 years old and still working. Maybe the longevity offsets the price.

The consensus of most boaters and marina tecs I have talked to that flooded is the way to go.

Unless you have a special needs..like a bluewater sailboat that may take a knockdown or an unusual battey space that requires wird mounting (on their side or something)...flooded can't be beat forgeneral use if COST IS a consideration.

Problems with charging are a function of your charging system and battery use...not the batteries. If you have problems with flooded...then you may have the same of other issues with AGMs.

Battery banks and charging systems can be very simple and carefree...or you can make them complicated trying to power your boat forever through a massive system that requires an EE degree to keep it functioning...not that that approach is bad...you just have to understand what is going on with YOUR system and most advice from others is useless unless you provide a detailed schematic and specs on every componenet.

I love my AGMs. One less thing... as Forrest would say. Install and forget.

I have a bank of 8 6 volt AGMs connected to a Magnum Energy inverter/charger that is 3 years old. I have never "equalized" them. Is it required or necessary?

I have never discharged them more than 25%.

AGM is recommend for house, not start. Floods are still the best for starting, 500 to 1000 vs. AGM of 650. If you compare the AGM with a flood Deep Cycle they compare about the same. Moat of the new floods have screw on caps which makes them less maintains. Also the charging requirements are different between flood and AGM which might require two chargers as I think AGM require a volts, and if you do not charge them correctly it voids the warranty, so make sure you have the correct charger.

My last flood last 7 years. So if you have flood start batteries, then you might was well have flood house. Oh, lastly for house Gel is rated higher than AGM as they have twice the charging cycle. AGM and Flood are about the same. In the West Marine catalog there is a table comparing the direct kind of batteries or go to a battery store and talk them about batteries.

I been there done that 3 times now and still with gook old cheap reliable flood batteries.

According to ProMariner, the manufacturer of the charger I bought to replace a failed Xantrex charger that could/would not be repaired by the company (that's a veiled dig if you missed it), AGM and flooded cell batteries can be charged by the same charger. After all, once you are off shore power and underway, they are being charged by the same alternator.

It's "gell" batteries that need different treatment. Most of us don't use gell batteries.

rwidman said:

Other than up front cost, there are no "cons" to AGM batteries for marine use. A lot of folks (including me) feel that the Sears Die Hard Platinum Marine group 31 AGM is the best without dealing with costly specialty batteries.

If you are building a boat, the additional cost of AGM batteries will be insignificant compared to the cost of the boat.

Click to expand...

I had wondered about those Sears batteries.My local Sears doesn't carry them but they have a display and can order them.I guess they don't stock them because few people around here use them.They are stuck on those crappy Walfart batteries.

Yeah,I'm kind of lucky on my boat build.I have a lot of resources available to me that will drastically lower my build cost,so I could spend some on other areas that I may other wise skimp on.

Fighterpilot said:

They have flooded battereis now days that are "sealed" in a limit fashion. No way to add water, and in theory, no need to. Since my start bank is almost impossible to get to I have a pair and will see how they work. Sam's sells them among others. My battery charger won't handle a mixture of batteries so I went cheap with the flooded batteries. Don't have a big load since we don't live aboard or camp, but I do have two 6 volts in series that do have covers that I can get off to service. They are easier to get to.

Click to expand...

I have used those before.The longest I have had them last is a couple of years.I'd rather have standard flooded if I go that route.I like being able to keep an eye on electrolyte levels.It's key to longevity.

Delfin said:

One advantage of AGMs that tipped me in that direction is their superior absorption rate. You can have all the charging capacity in the world, but if the batteries won't soak up the current you still spend a long time charging. Perhaps the higher cost is offset somewhat by less charging time than flooded.

Click to expand...

That is a selling point that I didn't think of last night when I made this post.I was tired and it shows.

Budds Outlet said:

We are beginning our 8th season with a set of Excide Orbital AGM batteries. One starting battery and two house batteries, all three manufactured in August of 2004.

We love the fact there is no unabsorbed acid. Absolutely no corrosion to battery terminals. No charging odor. No chance of spillage or leak or ruined battery trays.This is one reason I enjoy my current AGM batteries.

AGM's don't self discharge as rapidly as flooded batteries so they don't self distruct from sitting discharged as quickly.I have found this to be 100% true with my AGM equipment batteries.

Great to know they absorb charge faster than flooded. I'm a convert.That's always a huge plus.

Click to expand...

Scary said:

I can speak to longevity, the two 8d AGM's on my last boats thruster are over 8 years old and still working. Maybe the longevity offsets the price.

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I would think so.

psneeld said:

The consensus of most boaters and marina tecs I have talked to that flooded is the way to go.Most here push AGM but that may be due to the higher price thus more profit.

Unless you have a special needs..like a bluewater sailboat that may take a knockdown or an unusual battey space that requires wird mounting (on their side or something)...flooded can't be beat forgeneral use if COST IS a consideration.I had considered putting them in a locker,under the floor, in the rear cabin.

Problems with charging are a function of your charging system and battery use...not the batteries. If you have problems with flooded...then you may have the same of other issues with AGMs.

Battery banks and charging systems can be very simple and carefree...or you can make them complicated trying to power your boat forever through a massive system that requires an EE degree to keep it functioning...not that that approach is bad...you just have to understand what is going on with YOUR system and most advice from others is useless unless you provide a detailed schematic and specs on every componenet.Keeping it simple.I want to enjoy boating not messing with gadgets or watching something on a screen.

Click to expand...

Keith said:

I love my AGMs. One less thing... as Forrest would say. Install and forget.

Click to expand...

Good ole Forrest and the K.I.S.S. principle.

David O said:

I have a bank of 8 6 volt AGMs connected to a Magnum Energy inverter/charger that is 3 years old. I have never "equalized" them. Is it required or necessary?

I have never discharged them more than 25%.

Click to expand...

Thanks for your details.I had considered a dedicated inverter charger for the house bank.I'll have to see when I start laying out the electrical schematic for the boat.

I plan to research the equalization issue much further.My Trojan charger desulfates and equalizes flooded batteries.I know AGM can't be desulfated and I am unsure on the equalization issue.

Phil Fill said:

AGM is recommend for house, not start. Floods are still the best for starting, 500 to 1000 vs. AGM of 650. If you compare the AGM with a flood Deep Cycle they compare about the same. Moat of the new floods have screw on caps which makes them less maintains. Also the charging requirements are different between flood and AGM which might require two chargers as I think AGM require a volts, and if you do not charge them correctly it voids the warranty, so make sure you have the correct charger. If I use flooded, I would use the hydrolink caps and plumb a small tank with distilled water to them.


My last flood last 7 years. So if you have flood start batteries, then you might was well have flood house. Oh, lastly for house Gel is rated higher than AGM as they have twice the charging cycle. AGM and Flood are about the same. In the West Marine catalog there is a table comparing the direct kind of batteries or go to a battery store and talk them about batteries.I will check out West Marine's battery chart.

I been there done that 3 times now and still with gook old cheap reliable flood batteries.

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Thanks for all the input.A lot of good info.

If you choose the right AGM's, they are hard to beat for starting. They are not all the same. Some are designed for starting, some for "dual-purpose". A tiny 38lb Optima 34 red top or 34M blue top has 850 CCA. Two in parallel is 1700 CCA for 76 lb. My pairs lasted 7 years starting my boat's Volvo 44 diesel, and 10 years starting my Ram pickup's Cummins.

My paralleled pair of g31 "dual-purpose" Deka AGM's lasted 11 years as house bank.

When my wet cell acid batteries I got with the boat died, and I must admit they lasted ~8 yrs, I replaced the start batt with one big sucker truck-sized, wet cell but sealed, high cranking amp type, and the 2 house batts with AGMs. I have one small solar panel charging the start batt, and a purpose designed Ctek starter charger on it at the dock, and a larger multi-stage Ctek on the house batts, with air breeze and larger solar panel charging those two when out. They have all worked faultlessly, and I expect them to do so for a very long time. However the most enjoyment I get out of this arrangement is NOT HAVING TO GROVEL DOWN THERE AND CONTINUALLY TOP THEM UP.....'nuff said...?

Less maintenance equals more cruising which leads to more happiness.Stuff still breaks down and I enjoy being able to do my own repair work.I just don't wanna spend all my time maintaining systems and repairing break downs.

I have no problem with good wet cell batteries such as Trojan or Rolls. Due to the situation on Moonstruck, AGM batteries work best. My 510 amp/hr house bank consists of 2-8ds that have been located under the generator to save space. No maintenance is necessary, and the terminals and fuses are readily accessible. There has been no corrosion problems on the terminals. To keep all batteries the same type and age, they are all AGMs. I talked with Lifeline about starting batteries. I have 2 Group 31 series that do a great job of starting the 500hp Yanmars. A group 27 is on the 12kw Northern Lights generator.

The charger is also set for AGMs to charge at a higher rate, and they have faster absorption. They are quite expensive, but work for me I am upsizing my 40 amp charger to a 60 amp with the idea of a little faster charging time.

By the way, when underway the port engine 80 amp alternator charges the house bank, the starboard charges the starting bank. All banks are completely separate until a parallel switch is turned on to tie all batteries together for an emergency. I like this arrangement very much. No worries about one bank drawing the other down.

We can run the fridge and ice maker together over night for 12 hours with 75% capacity left in the house bank. We have electric cooking, so turn on the generator for that and charging in the morning. That will hold for a 12 hour day. Then run the generator for an hour and a half or so to heat hot water and cook. That charges the batteries for the evening. I do not like to discharge them below 60%. So goes life on Moonstruck.

Pioneer's Sonnenschein dryfit gel batteries are now 18 years old (I bought them used) and I have just had them tested and they're still as good as new. The tester guy reckons that gel cells are good for 30 years if well maintained - ie a proper charging regime.
Most people don't keep their boats that long so is it worth the extra cost - probably not - but if you can get from a battery reconditioner(desulfated) as I did, it certainly is.

Bendit said:

Pioneer's Sonnenschein dryfit gel batteries are now 18 years old (I bought them used) and I have just had them tested and they're still as good as new. The tester guy reckons that gel cells are good for 30 years if well maintained - ie a proper charging regime.
Most people don't keep their boats that long so is it worth the extra cost - probably not - but if you can get from a battery reconditioner(desulfated) as I did, it certainly is.

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Now, that's what I call getting service out of your batteries. If I ever order another new boat, gels will seriously be looked into. Thanks for the info. I had no idea that you could expect that kind of longevity from gels.

Marine shops in Oz (and probably anywhere) sell "Inox Battery Conditioner",claimed to get the sulfur off the plates of unsealed flooded batteries and back into solution where it belongs. Does it work? I think so, provided the battery is otherwise ok.
Best thing for long battery life is keeping it charged. Solar,through a good multistage regulator,works for us on our swing mooring.BruceK