SailNet Community - View Single Post - AGM batteries
Thread: AGM batteries
View Single Post
  #16  
Old 03-20-2013
Maine Sail's Avatar
Maine Sail Maine Sail is offline
Senior Member
 
Join Date: Jan 2003
Location: Maine Coast
Posts: 5,246
Thanks: 9
Thanked 107 Times in 78 Posts
Rep Power: 15
Maine Sail is just really nice Maine Sail is just really nice Maine Sail is just really nice Maine Sail is just really nice
Re: AGM batteries

Quote:
Originally Posted by chef2sail View Post
Maine...is this true?

•The higher charge efficiency of AGMs allows you to recharge with less energy: Flooded cells convert 15-20% of the electrical energy into heat instead of potential power. Gel-cells lose 10-16% but AGMs as little as 4%. The higher charge efficiency of AGMs can contribute to significant savings when it comes to the use of expensive renewable energy sources (wind generators, solar panels, etc.) as your charging system can be 15% smaller (or just charge faster).

I am not arguing with you about the use of AGM. There is a lot of misinformation printed then. I am able to get mine back up to 100% quickly, but eventually I will need to replace them, My 6 volt Lifelines are now 5 years old and going strong. Part of me using them is their inaccessability and that I have two laying on their sides.

This is not correct information then?

Battery Types: Flooded versus AGM and Gel
Dave,


You are using your AGM's for one of their actual "benefits", this is GOOD.. I RARELY see more than hand full of boaters taking advantage of any of the real pluses of AGM's..

Much of that information from that site is correct and much of it is very "dreamy"... For example that article is still in the "fantasy" stages of AGM technology where they sold us on 80% DOD's and suggested you could get away with a smaller bank. That marketing "tune" has changed big time..

This is straight from the Lifeline tech manual.

"For example, if 100 Ah is required on average, select at least a 200Ah battery. This approach will limit the average depth of discharge to 50% and will dramatically extend the life of the battery.

To get the best cycle life, the average depth of discharge should be as low as possible. Concorde (Lifeline) recommends the average depth of discharge be no greater than 50% of the battery’s 20 hour rating."


They are not recommending 3:1 bank sizing as that article insinuates, they are suggesting 2:1 bank sizing just as flooded batteries are sized for. I referenced this in the above post and it is 100% backed up by the AGM makers themselves, including Lifeline, which that article seems to tout. The only exception to this that I am aware of is Odyssey who still market at 80% DOD and 400 cycles.

This one element alone throws a HUGE monkey wrench into the entire bank sizing calculations for that site. It would also be better for the math if he had rated the T105's at what Trojan does, which is about 1200 cycles to 50% DOD.. It is right on the T105 Tech Data sheet.

One other thing I find rather odd or perhaps misleading is his use of the West Marine batteries in the cost comparisons. It is NOT a secret that WM slaps a Sea Volt sticker on Deka/East Penn batteries. They are the MOST EXPENSIVE reseller of these batteries or put another way that Sea Volt sticker is VERY expensive.....

Heck the Group 31 12V Deep Cycle was selling for $247.99 in last yeas catalog. That SAME battery can be purchased at Sam's Club for $84.97..

Sams Club = Group 29/31 (Deka DC31) 105Ah Battery $84.97

West Marine = Group 31 (Deka DC31) 105Ah Battery $247.99


Difference = $165.02 per battery !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I honestly wonder how the math would have worked out had he compared the least expensive re-seller of the SAME battery rather than the MOST expensive......????? Inquiring mids are curious...

The SAME batteries can be purchased at NAPA, O'reilly Auto, Sam's Club and many other locations for considerably less than HALF the cost of West Marine. Of course on the flip side, if you use West Marine as your basis for cost analysis, it helps make the Lifeline Battery look better...

AGM's charge faster. No secret there and I DO take advantage of this on many installations. Where customers CAN take advantages of the faster charge, and they fully understand that life cycles may not be as good as they suspect, I have no issues installing AGM's and in many cases actually recommend them..

Another big problem is that most boats I go on can't even meet the minimum suggested charge capacity for AGM's, 40% of "C" for Odyssey and 20% of "C" for Lifeline so it makes very little sense to spend huge money on a system we already know will be on the short side of longevity by having a limited charging system.

The other "never talked about" issue is that when AGM's are new they take GOBS of current. New however does not last very long if the batteries do not get back to 100% after every discharge cycle. For mooring sailors this a tough issue. Lifeline specifically notes this in their warranty.

"The limited warranty does not cover discharged batteries, batteries that have been opened, frozen, sulfated batteries due to undercharging, diminishing capacity due to battery age, split open battery cases, transportation, rental, testing, housing, freight or installation costs."

Back in the real world, not warranties worth about as much as the paper they are printed on, I have a 4 year old bank of Lifeline 6V batteries to replace in the next month. They are currently taking just 65-80A in bulk/in-rush and hitting absorption voltage within a few minutes. The alternator, when loaded, goes right up to its 150A cold rating. Customer initially blamed the alternator and regulator and spent HUGE money having the alternator re-built and purchasing a new replacement regulator. Same issue... He calls in the boat yard, they diagnose it as poor wiring and replace it to the tune of $1600.00. OUCH!!! Same problem. Finally I get a call show up, test the batteries, measure internal resistance, fire up the motor and say: "you need new batteries".... "But they are only 4 years old, it can't be the batteries.".... I plug my heat gun into the inverter, fire up the motor and put my Fluke around the alternator output wire. What would you know 150A and the alt and reg are working just fine. Turn off the heat gun and right back to 65A of acceptance..... As it sits now this bank of four 6V batteries takes about 12+ hours to get to a full charge due to the sulfation. So yes when new, how all the marketing is done, they can and do charge faster. However unlike flooded or GEL cells they really don't like to sit at anything less than 100% SOC or they sulfate and performance, including charging performance, suffers and seems to suffer faster than with GEL or flooded LA batts..

From Lifeline:
"For repetitive deep cycling, chargers should have an output current of at least 0.2C (20 Amps for a 100 Ah battery). If the output current is less than this value, the cycle life of the battery may be negatively affected."



Hell beyond the initial 3:1 bank sizing or 80% DOD we were sold on, we were also led to believe early on that AGM batteries did not even sulfate.. Talk about marketing. I can clearly remember the marketing guys telling me "you never need to equalize an AGM battery because they don't suffer from sulfation." SWEET!! So I went out and installed a few banks, based on the "glossy marketing"....... Hmmm guess what? They sulfated..... Doh'........

With AGM's I hear so many people claim they bought them for "high acceptance rates" then they feed a 450Ah bank with an 80A alt that when hot puts out 60-65A or about 14% of capacity or 6% below the minimum suggested by Lifeline.

Heck that same bank in flooded batteries will take the full hot capacity of a 125A alternator or slightly more..

Back in the real world I work in, a customer just last month called me to ask if he really needed to be there for the 8 hours he was going to be equalizing his Lifelines for. Ummmm YES, how else are you going to monitor the battery temperature during this over voltage event....!!!! Makes adding distilled water to some flooded cells seem like cake walk.... 8 hours of 15.5V for a "conditioning charge", but they are sold as "no maintenance". At year two he is already noticing "diminished capacity" hence the conditioning charge. That said AGM batteries are this customers best option due to fitment, containment and because he actually has a 180A alternator. Cost is not an issue for him.

Again, AGM's HAVE NUMEROUS benefits its just that cost and cycle life are not either of them....
__________________
______
-Maine Sail / CS-36T


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.




© Images In Posts Property of Compass Marine Inc.



Last edited by Maine Sail; 03-20-2013 at 10:43 PM.
Reply With Quote Share with Facebook