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shootandfish1's avatar
shootandfish1
Explorer
Oct 04, 2014

AGM Battery Discussion-Discharge/Charge Cycles

OK, Let us agree to no FLA vs AGM is better comments. AGM ONLY!!! And this discussion is aimed mainly for my fishing boat (still an RV-Right!!!), but applicable to any DC deep cycle purpose. And this group of 'Experts' are the most technical bunch of folks known;)

I'm researching batteries for the more powerful trolling motors, 80-112 lb thrust, 24-36 volt. Boat desperately needs more weight as far forward towards the bow as I can practically place 2-3 12 volts. Since this is where most of the 'pounding' takes place (both on the water and towing), I feel that AGM's are better suited than FLA Batteries for this purpose.

I was (still am) looking strongly at the Sam's Club Duracell AGM Gr 31, which is the same as Deka's (East Penn) AGM Gr 31, 105 Ah@20Hr rate, 69 Lb. My research indicates that the SC Duracell is very good choice for the price and equally important is that a Sam's Club is located in about every town near my intended fishing and camping trips (SE USA, mainly Florida).

East Penn has a wonderful pdf discussing the care of AGM and Gel Batteries. On p 10 is a chart showing that a Deka AGM should be good for 370 cycles for a 50% DOD and 200 cycles for a 80% DOD. (Gel Batteries have much better numbers, but I fear difficulty in obtaining 'fresh' batteries at a reasonable cost and SC stocks the AGM Gr 31 should I need a replacement.

After various on-line searches, I came across Cabelas 900-X AGM made by NorthStar, also available in a Gr 31, 101 Ah@20Hr rate, 76 Lb. NorthStar is stating that their AGM is good for 900 cycles @ 50% DOD and 400 cycles @ 80% DOD!!!!

Is NorthStar's advertised cycles for stated DOD's reasonable? I understand that correct charging is necessary for a battery to perform, but over double the cycles at 50% DOD and double at 80% DOD is quite a strong statement for 2 almost equally (by weight) batteries.

The Northstar's Gr. 31 is about twice the cost of the SC Duracell, so the cost per Ah and cycle are actally quite close. $179 compared to $385ish. Taxes and shipping costs yet to be factored in.

Did not mean to be so 'long-winded', but curious to what the 'Pro's' here think. Hope and pray that my links work.

Fred


Deka Tech Manual For AGM & Gel Batteries

Deka Marine/RV AGM

Sam's Club-Duracell AGM Deep Cycle Marine/RV Gr31

NorthStar Marine/RV AGM Gr 31

Cabelas 900-X AGM Gr 31

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  • mena661's avatar
    mena661
    Explorer
    Oct 04, 2014
    shootandfish1 wrote:
    OK, Let us agree to no FLA vs AGM is better comments.
    Eventually this will turn into that. All of the AGM threads seem to.
  • shootandfish1's avatar
    shootandfish1
    Explorer
    Oct 04, 2014
    Thanks for the replies. Did a search and a Lifeline dealer is within a reasonable drive.

    On Lifeline's website, found the linked manual. Very quickly skimmed thru and on the last page, p 38 found a graph comparing cycles to DOD.
    Interesting--

    At 50% DOD---1000 cycles

    At 80% DOD---550 cycles

    Lifeline Manual

    Curious as what a Gr 31 Marine will cost?

    I will have to weigh cost per Ah, cost per cycle, ease of replacement, warranty, and hate to say this, cost of replacement due theft. Boats and associated equipment are prime and, despite precautions, are fairly easy targets for crooks. (Florida fishing areas seem to be a 'hot-bed' for boats, outboards, trailers, generators, and ...Yeti/Pelican/Engel coolers dissapearing.)

    I want to discuss proper charging in a separate posting and after studing East Penn's Tech Manual. I know that a proper charger is mandated. First problem is a 'Marine', i.e. waterproof and sealed chager is required (open boat). I'm a little fuzzy after looking at so much info, but it seems like 15 Amps per battery is the largest I've seen.

    Fred
  • landyacht318's avatar
    landyacht318
    Explorer
    Oct 04, 2014
    How are you planning on recharging them?

    I didn't peruse the Deka, but are they not limited to no more than 30 amps per 100 amp hours?

    Northstar is a little more vague on minimum bulk charge amperages, I've been using Odyssey's Specs, because they make many of the same claims.

    Odyssey says their group 31, rated at 100 AH, when cycled deeply, absolutely requires 40 amps minimum until 14.7v is attained, then 14.7v is to be held for 4 hours. Get three of these and you need 120 amps and a charger capable of 14.7.
    Odyssey® Battery Technical Manual – Seventh Edition

    Sears Die hard platinum are rebadged odyssey. Their group 31 goes on sale every so often for 230ish$

    I have a Northstar. They say that 12.1v is 50%. last time I took 55 A/H from it( 90 amp hours total) it was still reading 12.2v under a 4.5 amp load. Fully charged resting open circuit voltage on my group 27 is 13.06v.

    I think the NorthStar is under rated capacity wise, and when I use it to start my engine, it cranks it faster than two group 27 marine batteries did previously.

    I've not had a deka AGM, but I am impressed with the Northstar, but I don't think it would be a good low and slow recharge solar battery.

    The NS has responded well to high amp charge currents of 35+ amps. Much better than 25 amps, and way better than the ~12 amps my solar can do.

    I'd still pad their bases if they are going to be beat up mid boat.

    Batteries plus re-badges a Northstar as X2 Power and adds a year to the warranty.

    Lifeline AGM is likely still top dog AGM
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Oct 04, 2014
    My B.S. detector is quivering...

    Lifeline, made by Concorde is considered the gold standard in the industry. By experts. Sort of like Rolls & Surrette for flooded batteries. The Concorde battery cycle DOD chart does not come close to the "Northstar". Personally I have never heard of this brand and manufacturing an AGM battery is a big enterprise.

    This battery would just about having to be manufactured overseas, with Germany being a top guess. Home of Sonnenschein and other top originators of accumulator quality. To put it bluntly the chances of me venturing forth and blindly putting my money on a mysterious brand battery making rather robust claims is well, near zero. Of course this is my opinion based on my own needs and wants.

    I've seen a lot of battery braggadocio come and go in the last 50 years. You may consider me a skeptic about wild claims. There is only so much room in a group 31 jar. Fitting plates, envelope separator glass mats and cell connectors leaves only so much extra space. Concorde claims it has squeezed out the last mm of available space. After giving their technology the eleventh and twenty sixth over, I would have to agree. Where does this leave the North Star claims in my humble opinion?

    Coming back down to reality I think your choice is a good one regarding battery type. I would myself, choose an accumulator that fit my budget, and seemingly has the best service and warranty procedures. If my goal was the longest lived battery I would take a hard look at Concorde's Lifeline. There is no thinner AGM positive plate that is going to outlive Concorde's .115" positive plate. That and they are the only OEM that uses AGM envelope separators which stop plate mossing shorts which is hyper critical when plates and mats are stuffed as tight as they are in the Lifeline.

    But all of this is my opinion. Most importantly, the AGM is going to give you a solid uptick with electric motor operation. In fact I would have to say flooded batteries here would be inappropriate.

    Hope this helps
  • westend's avatar
    westend
    Explorer
    Oct 04, 2014
    I would opine that Deka's ratings are more conservative and that Northstar's ratings are more liberal. If it was me, I'd get the Duracell's from SC for all the reasons you gave and because I believe East Penn/Deka makes damn fine batteries.
    Disclaimer: I own 3 Deka's and have also read the literature.

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