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  #1  
Old 03-19-2013
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AGM batteries

I have a few questions I am thinking someone out there knows the answers to. My boat came with three group 27 AGM batteries with two in a house bank and one as a starter battery for my Perkins 4.108. I would like to combine the three current batteries into the house bank and buy an actual starter battery for the diesel.

My house bank currently resides in two typical battery container boxes and if I try to put the third in the same area it would not fit in its own box. Do AGM batteries need to be in boxes or just secured? If they need to be in boxes I will likely fabricate a box that fits all three.

I am thinking of getting a typical lead acid starter battery for the diesel. I'm wondering if I'll have a problem in mixing batteries between the two systems. I never allow both banks to interact and have a separate charging system for both when I'm plugged in to shore. The problem I think might occur when the ACR combines the bank when I'm charging while motoring. Any thoughts on this?

Also, any recommendations on the size of a starter battery I'll need?

Thanks

Scott
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Old 03-19-2013
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Re: AGM batteries

AGMs need to be secured. Doesn't hurt to put them in a box, either.

A group 27 start battery would work. I use a group 31 start battery for my 4-108 just for a bit of extra capacity.

AGMs and flooded batteries have almost identical charging profiles, so you could use a flooded start battery.

Not sure how your ACR is wired. The ideal way these days is to lead ALL charging sources to the house battery bank, then use either a voltage-follower device (e.g., EchoCharge or DuoCharge) or an ACR to maintain the start battery.

BTW, start batteries require very little charging. Starting your 4-108 typically will use 150-175A while cranking, but only for a very few seconds. Typical capacity draw for a diesel start is less than 0.5 amp-hours!! This is replaced in just a couple of minutes.

Bill
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Old 03-19-2013
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Re: AGM batteries

Quote:
Originally Posted by btrayfors View Post
AGMs need to be secured. Doesn't hurt to put them in a box, either.

A group 27 start battery would work. I use a group 31 start battery for my 4-108 just for a bit of extra capacity.

AGMs and flooded batteries have almost identical charging profiles, so you could use a flooded start battery.

Not sure how your ACR is wired. The ideal way these days is to lead ALL charging sources to the house battery bank, then use either a voltage-follower device (e.g., EchoCharge or DuoCharge) or an ACR to maintain the start battery.

BTW, start batteries require very little charging. Starting your 4-108 typically will use 150-175A while cranking, but only for a very few seconds. Typical capacity draw for a diesel start is less than 0.5 amp-hours!! This is replaced in just a couple of minutes.

Bill
Hey Bill

SO would you use the wet cell charge cycle for both or the agm charge cycle for both?

Brian
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Old 03-19-2013
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Re: AGM batteries

I used to have the starting battery echo charged off the house bank like Bill mentioned, but with the ACR I installed it acts like an isolator and combiner so that wasnt necessary

Peronally I dont like mixing types of batteries, but because the wets take about the same bulk charge as AGM and its the starter battery whoich woint be discharged much, it may be ok but I am not an expert. Will the AGM be held back by the wet cell charge acceptance?

Dave
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Old 03-19-2013
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Re: AGM batteries

The ONLY way that I would consider mixing AGM and Wet-Cell batteries, of different ages, is with the HOUSE bank as AGMs, and the START battery connected via an Echo-Charge. I would verify that the voltage regulator is capable of working with AGMs, and that your alternator is up to the task of charging the house bank. The battery switch would be switched to the start bank to start, and then quickly switched to the house bank at any time when the engine is running.

In general, my learning from the posts in SailNet, and elsewhere, is that one should not mix battery types. YMMV

AGMs do not need to be kept in a box, they only need to be secured.

Good article here: http://www.pacificpowerbatteries.com/marinebatts.html
Quote:
AGM Pro's: better cycling and depth of dischager over the wet or gell batteries. While most wet batteries are supposed to only go to about 50% depth of discharge, the AGM's are able to go to about 20% depth of discharge without harming them PROVIDED that you don't overcharge them at too high a voltage on their return.
...
Quote:
Wet Lead Acid Battery Con's: Slower to recharge than AGM, require maintenance more often, and don't cycle as deeply as the AGM batteries.
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Old 03-19-2013
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Re: AGM batteries

Quote:
Originally Posted by eherlihy View Post
The ONLY way that I would consider mixing AGM and Wet-Cell batteries, of different ages, is with the HOUSE bank as AGMs, and the START battery connected via an Echo-Charge. I would verify that the voltage regulator is capable of working with AGMs, and that your alternator is up to the task of charging the house bank. The battery switch would be switched to the start bank to start, and then quickly switched to the house bank at any time when the engine is running.

In general, my learning from the posts in SailNet, and elsewhere, is that one should not mix battery types. YMMV

AGMs do not need to be kept in a box, they only need to be secured.

Good article here: Pacific Power Batteries - About Automotive Batteries


AGM Pro's: better cycling and depth of dischager over the wet or gell batteries. While most wet batteries are supposed to only go to about 50% depth of discharge, the AGM's are able to go to about 20% depth of discharge without harming them PROVIDED that you don't overcharge them at too high a voltage on their return.
...
This is what is so frustrating about the internet, that poor information, is trumpeted as truth..

That data was EXACTLY how AGM batteries marketed and launched themselves into the marine market. Those bogus promises of longer cycle life and more usable capacity than deep cycle flooded batteries was soon ousted as a mistruth in the "real world" where the battery life really matters.. These misleading marketing attempts really bit them in the ARSE because cycle life at 80% DOD SUCKED....

Today nearly every maker of AGM batteries, Lifeline, Deka/East Penn (and all their private labels), Trojan, Rolls etc. etc. all recommend a 50% DOD not 80% DOD.

Odyssey still sells on 80% DOD but they readily admit that at 80% DOD you only get 400 cycles. (and this in in a laboratory with white glove treatment)

At 80% DOD with a flooded group 31 Rolls 12V battery you get 800 cycles or DOUBLE the life of an Odyssey AGM at 80% DOD. DOUBLE the rated cycles !!!! The Rolls battery also costs less than HALF of what an Odyssey does.

With a Deka/East Penn AGM group 31 12V battery you get 250 cycles to 80% DOD.

Compare that to a US Battery DCXC group 31 flooded deep cycle battery that sells for about $120.00 and it gives you 675 cycles at 80% DOD!! Bump that up to 50% DOD and you get 1150 cycles yet the Odyssey only gives 700 at 50% and the Deka/East Penn 500 cycles at 50% DOD..

Oh and to even attempt to come close to 400 cycles at 80% DOD with Odyssey batteries you need a minimum of 40% of capacity in charging current. So a 400Ah bank needs a charge source capable of maintaining 160A. If this is an alternator you'd need a cold rating of about 200A to have 160A when hot.... How many boaters can do that or expend all that money just to hope they "might" get 400 cycles when a cheap $120.00 battery will give 675 cycles with no fancy charging system upgrades.....

The fact is that AGM's do not offer longer life or deeper cycling an this has been priven time and time again in the "real world" and also in the lab by the manufacturers.. The manufacturers own data shows shows this, it's where I got the numbers from above.

I find this to be an interesting quote by Trojan Battery. When AGM's first came out the claims were BETTER cycle life than wets as that web site still seems to claim..

Quote:
Originally Posted by Trojan Battery
Generally, gel and AGM batteries have about 20% less capacity, cost about two times more, and have a shorter cycle life than comparable flooded lead acid batteries. However, Gel and AGM batteries do not need watering, are safer (no acid spilling out), can be placed in a variety of positions, have a slower self-discharge characteristic, and are more efficient in charging and discharging than flooded batteries (see table below). Gel batteries are more suitable for deep cycling applications whereas AGM batteries are more for light cycling and engine-starting applications.


Disclaimer: Keep in mind that ALL of those numbers are LAB DERIVED where temperature, charge rate and charge/discharge cycles are done very methodically and repeatably. Those numbers are NOT at all indicative of what you'll see in the real world. If you want real world numbers chop 50% right off the top and now you're in the ball park..
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Last edited by Maine Sail; 03-19-2013 at 04:00 PM.
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Old 03-19-2013
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Re: AGM batteries

Quote:
Originally Posted by Maine Sail View Post
This is what is so frustrating about the internet that gobledey goook is just that..

That data was EXACTLY how AGM batteries marketed and launched themselves into the marine market. Those bogus promises of longer cycle life and more usable capacity than deep cycle flooded batteries was soon ousted as a mistruth in the "real world" where the battery life really matters.. These misleading marketing attempts really bit them in the ARSE because cycle life at 80% DOD SUCKED....

Today nearly every maker of AGM batteries, Lifeline, Deka/East Penn (and all their private labels), Trojan, Rolls etc. etc. all recommend a 50% DOD not 80% DOD.

Odyssey still sells on 80% DOD but they readily admit that at 80% DOD you only get 400 cycles. (and this in in a laboratory with white glove treatment)

At 80% DOD with a flooded group 31 Rolls 12V battery you get 800 cycles or DOUBLE the life of an Odyssey AGM at 80% DOD. DOUBLE the rated cycles !!!! The Rolls battery also costs less than HALF of what an Odyssey does.

With a Deka/East Penn AGM group 31 12V battery you get 250 cycles to 80% DOD.

Compare that to a US Battery DCXC group 31 flooded deep cycle battery that sells for about $120.00 and it gives you 675 cycles at 80% DOD!! Bump that up to 50% DOD and you get 1150 cycles yet the Odyssey only gives 700 at 50% and the Deka/East Penn 500 cycles at 50% DOD..

Oh and to even attempt to come close to 400 cycles at 80% DOD with Odyssey batteries you need a minimum of 40% of capacity in charging current. So a 400Ah bank needs a charge source capable of maintaining 160A. If this is an alternator you'd need a cold rating of about 200A to have 160A when hot.... How many boaters can do that or expend all that money just to hope they "might" get 400 cycles when a cheap $120.00 battery will give 675 cycles with no fancy charging system upgrades.....

The fact is that AGM's do not offer longer life or deeper cycling an this has been priven time and time again in the "real world" and also in the lab by the manufacturers.. The manufacturers own data shows shows this, it's where I got the numbers from above.

I find this to be an interesting quote by Trojan Battery. When AGM's first came out the claims were BETTER cycle life than wets as that web site still seems to claim..





Disclaimer: Keep in mind that ALL of those numbers are LAB DERIVED where temperature, charge rate and charge/discharge cycles are done very methodically and repeatably. Those numbers are NOT at all indicative of what you'll see in the real world. If you want real world numbers chop 50% right off the top and now you're in the ball park..
Have I told you that my Lifelines have now been replaced with a cheap set of wet cells.... hmmmm... (most certainly agree with you Maine).

Only stipulation I will add is that for some installs, agms seem a better choice. THis is where the batteries may not set up straight or are difficult to get to for maintenance. But for cruisers, who rarely get their batts back up too 100% soc, agms are an awfully expensive experiment in dissapointment.

Brian
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Re: AGM batteries

Brian,

I'd set the charger and any regulator(s) --- for the alternator, wind generator, solar panels, etc. --- to the AGM profile. The EchoCharge will take care of the flooded start battery just fine.

And, if you set it up as I suggested with all charging sources going directly to the house battery bank, with an EchoCharge or DuoCharge connected between the house bank and start battery, then there's no need for switching at all.

IMHO, it's a BAD IDEA to play with the main battery switch while the engine is running, even if it has a field disconnect circuit. Someday, you or one of your crew is going to switch to the wrong position and blow your alternator diodes.

I agree with MainSail's comments about AGMs. Been running some factory supplied numbers myself. My conclusion at this point is that there are very few boats for which AGMs make any sense at all. If you really need a battery with a low self-discharge rate which doesn't require maintenance and which can be installed on its side, then go with gelled batteries.

These have a very long cycle life, provided that you properly set up the charging voltages. Just about any modern charger or regulator has this capability.

Bill
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Re: AGM batteries

Quote:
Originally Posted by Cruisingdad View Post
Have I told you that my Lifelines have now been replaced with a cheap set of wet cells.... hmmmm... (most certainly agree with you Maine).

Only stipulation I will add is that for some installs, agms seem a better choice. THis is where the batteries may not set up straight or are difficult to get to for maintenance. But for cruisers, who rarely get their batts back up too 100% soc, agms are an awfully expensive experiment in dissapointment.

Brian
Brian,

AGM batts have numerous benefits, they really do, but price & cycle life are not two of them..
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Re: AGM batteries

Scott, when batteries are combined into a bank it is best if they are all same size form the same production lot. Mixing batteries of different age, or batteries that have been cycled differently and are no longer in the same capacity, is not a good idea. They will equalize across each other and the weakest one will just pull down the others.

So if you have three "identical" batteries but one was used for starting and the other two for house? Don't combine them. Use 'em up, as they are, and then start fresh with one house bank of whatever capacity you want (or can find or afford) and one starting battery of the same chemistry so they can charge together on the same system.

While you are waiting for the current batteries to be used up, take a thorough look at your charging system, and plan to update, modify, improve, that as needed at the same time. Since the "little things" can literally double the life of your batteries, and batteries have gotten damned expensive, any money you spend optimizing the charging system is likely to be very well spent. Even if you optimize that now, and defer the new batteries until these are used up.
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