Place(s) to buy AGM battery for best pricing.

Discussion in 'Power - Site Power/Batteries/Generators/Solar' started by davekro, Nov 12, 2019.

  1. davekro

    davekro Active Member

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    I think I want to upgrade my old (now low capacity) AGM Grp 27 with a new AGM Grp 27 or 31. Is there a better place to find lower pricing for quality, known brand AMG batteries than Amazon? Anyone know if there might be Black Friday deals on AGM batteries (Amazon, other)?

    Looking at Amazon I see two seemingly decent choices with good ratings and a fair amount of raters. Any thoughts on these two in particular or other recommendations?

    1) Weize ≈Grp 27, 100AH*, LFP12100, $159 Amazon, 5 Star/60 ratings.

    2) Vmax Grp 31, 120AH, MR137-120, $279 Amazon, 4.4 Star/36 ratings.

    Since you should only run to 50% of capacity to not unduly shorten the # of cycles over the battery's life, you'd expect a theoretical 50 AH from the smaller Grp 27 battery and 60 AH from the Grp 31, right? If so, the 75% higher (+$120) priced Grp 31 theoretically gives you an extra 20% of amp hour use (60 vs 50). Is the lower priced battery the obvious choice, or is there a consideration I'm not thinking of? Of course, two Grp 27's would cost $318 or only 14% more than the Grp 31, theoretically yielding 100 AH to get to 50% SOC. I don't really know if 50% of AH really correlates to 50% SOC though.


    * One Amazon responder questioned Weize's rating using 10 hours, vs a 20 hour standard. Can anyone explain what that means in actual amp hour run time or affect this decision?
    "The standard for battery ratings is 20 hours NOT 10 hours like this battery. It is false rated to catch you if you're not paying attention and make you think it's a normal 100ah battery. IT is not, you are getting a 50 amp hour battery actually if you use the STANDARD amp hour measurement of 20 hours. Why is this battery False rated ? Is it to catch people off guard and getting half the battery they thought they were buying? see less
    By Amazon Customer on November 11, 2019"
     
  2. rabird

    rabird Howdy!

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    I hope this chart disproves what Amazon Customer stated.
    amp hr capacity, 20 hr. Room temp the battery is discharged down to 10.5v or so at a constant current and timed. Repeat for different current. Repeat Curve fit data and use formula to determine 20 hr capacity.

    look at this chart, the first is G24 battery, note at bottom the 20 hr capacity is 69 ah.
    now look at the 6A discharge and note it takes 10.7 hrs with a capacity of 64 ah. So the 10.7 hr capacity is 64 ah which is less than 20 hr capacity of 69 ah. 69/20 = 3.45A constant discharge for 20 hrs.

    battery.jpg

    check sams/costco for duracell AGM G31
     
    Last edited: Nov 12, 2019
  3. SteveP

    SteveP Well-Known Member

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    Battery capacity varies by the discharge rate. A battery discharged at constant 5 amps will output more amps than if discharged at constant 10 amps. So you would expect a battery that outputs 100 AH at 20 hour rate to only output about 93 amps at the 10 hour rate. By stating "100 AH @ 10 hour rate" They're making a veiled claim that their battery is superior to one that outputs 100 AH @ 20 hour rate. The question is, do you believe it? Is it achievable in the real world?

    The amazon customer is probably confusing amp hours with reserve capacity. Which is rated by discharge rate and results in minutes of run time. RC is normally stated at 25 amp discharge rate, RC @ 25 amps = 140 minutes. But I've seen battery advertisements stating RC at 10 or even 5 amp rates, which definitely skews the result.
     
  4. tenttrailer

    tenttrailer Art & Joyce - Columbus, O

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    Several years ago, Sams Club had the best deal on AGM G-31 batteries. There 105 AH AGM battery right mow is $179. It use to ne in somewhere around OCT, NOV of each year they would have a sale on the batteries. It's the same battery that west marine sells for about 275
     
  5. davekro

    davekro Active Member

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    Rabird, thanks for the info. Costco does not seem to carry AGM RV, maybe just the marine starting deep cycle combo. But reading reviews on the Duracell RV Deep Cycle's looks really good and great pricing. Duracell's G27 & G31 are actually pretty close in size and weight. Also, the Duracell G31 is only 67.5 lbs compared to the Vmax G31 I mentioned above. That is a plus for me because I'd double use that battery for running a raft w/ 12v trolling motor. So carrying between front driveway and back yard at the water.

    • Duracell AGM Marine Battery - Group Size 27M, Item # 980025493, Model # 27M, $159.
    https://www.samsclub.com/p/marine-27magm-18-mo-free/prod21234614

    Duracell AGM Deep Cycle Marine and RV Battery - Group Size 31, Item # 347736, Model # 31, $180.

    https://www.samsclub.com/p/duracell...size-31dtmagm/prod3590232?xid=plp_product_1_2

    "amp hr capacity, 20 hr. Room temp the battery is discharged down to 10.5v or so at a constant current and timed. Repeat for different current. Repeat Curve fit data and use formula to determine 20 hr capacity."
    Does the chart show that all batteries were drawn down to 10.5 volts? In your example of a constant 6 amp load, it took 10.7 hours to draw down to 10.5 v and used 64 AH of the battery's entire capacity (to dead, to essentially no usable voltage)? So if the G24 happened to have a 75 AH rating, it would have used 85% of that 75 AH? That does not look right. Is the AH column what is 'left' after 'x' hours at 'x' volts? Doesn't look quite right either because draining to 10.5 v is WAY below 0% SOC. I'm confused. ;o)

    Anyway, thanks for the lead to Sam's club. It's 45 mins away from me and I'm not a member. But I think my neighbor might be. ;o)
     
  6. rabird

    rabird Howdy!

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    in these test 10.5v under whatever load is considered DEAD or 0% SoC.


    Reserve Capacity (RC)
    1. Allow fully charged battery to stand at room temperature for 4 to 96 hours.
    2. Discharge battery at 25A at 80 +/- 5 degrees F (27 +/-3 degrees C).
    3. Determine discharge time in minutes to 10.5V for a nominal 12V battery.
    4. Correction for final discharge temperature: Mc=Mr[1-0.009(Tfinal-27)]
    Mc = minutes corrected to 27 degrees C (80 degrees F)
    Mr = minutes actually run
    Tfinal = temperature of electrolyte above plates in a intermediate plate in degrees C
    0.009 = temperature correction factor
    AH capacity (AH)
    1. Follow procedure for RC test except run at designated discharge rate (either n hour discharge rate or at specified amps). For example 20 hour capacity would be tested at nominal 20 hour discharge rate, i.e., 20 hour capacity in AH divided by 20 hours (105AH/ 20 hours = 5.25 amps. AH capacity may also be determined at a specified amp discharge rate, say 1, 5, or 10 amps, etc. The rating system is specified by the battery manufacturer. JCI marine batteries are normally rated at the 1A discharge rate.
    2. Upon determining the discharge time to 10.5V in miniutes. Convert to AH with the formula: AH = Mr X A / 60, where
    Mr = minutes actually run
    A = discharge rate in amps
    3. AH capacity available in the field is temperature and rate dependent and could deviate significantly from the rated value. Increased AH's are available at warmer temperatures and lower discharge rates.
     
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  7. tenttrailer

    tenttrailer Art & Joyce - Columbus, O

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    Yes 10.5 all. The AH and RC standard is Just that a standard that is to be used if rating a battery for AH's. It defines how how the voltage should be dropped, the temperature etc.... for the test.
     
  8. MNTCamper

    MNTCamper Well-Known Member

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    I would third checking out the Sam's club batteries. They are Duracell brand, which is East Penn (DEKA). Price as stated above and about 4-5 times a year, you can purchase them for an additional $20 off. I have the G31 FLA on my pop up and it works great. (Duracell) We can go for 10 days on this battery, but we don't draw a lot other than recharging stuff and lights.
     
  9. davekro

    davekro Active Member

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    Good to know to look out for $20 off Sam's Club battery sales. Does Sam's Club send paper or email sale adds to members to notify you of these sales? My neighbor is the Sam's Club member I'll be buying through. I'll ask him about if he gets sales adds.

    Someone on another thread said I might get more bang for the buck with a traditional whetted lead acid battery vs. an AGM lead acid. I can't see how that would be true for THIS Duracell group 31 AGM at the Sam's Club low price of $180. Maybe he was thinking/comparing too much more costly AGM batteries?? I'd think this is the best bang for the AH buck as well as best AH bang per pound (I'll be moving this battery to use on a raft occasionally in the summer).
     
  10. Econ

    Econ Well-Known Member

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    Crown battery and Trojan are considered upper quality batteries by most. The marketing manager for Crown said that the Lead Acid battery is a superior design to the AMG. The only reason to buy an AMG was your willing to sacrifice everything for a non off gassing battery.

    There are two different types of plates; rolled and stamped. I am pretty sure it is stamped that is the less favorable form of making and the type Costco and Sam's use. Trojan and Crown use rolled.

    Six months ago I did the math. The Trojan costs the same on a per year basis BUT it costs more up front because they last about 8 years.

    I'm going Trojan next time as Crowns are hard to get.
     
  11. davekro

    davekro Active Member

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    I just noticed in the specs for the $180 Sam's Duracell AGM 31 that it says it is an SLI (Starting, Lighting and Ignition). I had assumed it was a True Deep Cycle. Dual Purpose is the compromise between SLI and True Deep Cycle. I was looking to get a True Deep Cycle. I don't need the CCA compromise.

    One reason I was considering AGM was because they are said to charge back up faster, but is the difference significant (10%, 25%, 50% faster?). AGM is also said to tolerate deep discharge better than flooded. I guess dropping below 50% SOC shortens the life span of both, but again is the difference significant.* If I limited running my generator for two hours with a stand-alone battery charger set at 30amps, would the AGM recover significantly more SOC than the flooded version in that time?
    *For the sake of discussion, let's assume batteries are run well below 50% SOC accidentally occasionally due to out of sight out of mind when not in use.

    This YouTube was generally helpful, but with no specifics. :/
     
  12. Econ

    Econ Well-Known Member

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  13. GreyFox

    GreyFox Well-Known Member

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    Better make sure you have an appropriate charger for Trojans which require an unusual bulk charging voltage of 14.8 volts vs the more commonly recommended bulk charging voltage of 14.4 volts. ;)

    FWIW, so-called Duracell flooded batteries, AGMs, GELs are in fact manufactured by East Penn, the largest battery manufacturer in the US. Here in Canada they're sold at 60+ RV Care dealerships under the Traveler's Choice name - but they're the identical batteries. Bought a Group 31 myself. [A]
     
  14. rabird

    rabird Howdy!

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    where's your G31DC documentation on charging?
     
  15. davekro

    davekro Active Member

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    So what Rae the specs of the battery you bought? Flooded, AGM, GEL? Does it have a CCA rating? What map hour rating (the important spec)? Obviously RV ‘house’ batteries do not need CCA and I was under the impression that RV deep cylcle (not dual purpose) batteries did not even come with a CCA rating, or if it was rated, is was a very low # compared to a dual purpose deep cycle’s CCA rating like I have always used in my Mastercraft slalom ski boat.

    I was concerned to see the “deep cycle” Sam’s Club $180 AGM I listed above says in the specs it has 800 CCA and is listed as SLI (starting, lighting & instruments).
     
  16. davekro

    davekro Active Member

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    This article says AGM is not the end all be all they are purported to be. I’ll see what Sam’s Club might have in a Duracell flooded 12v group 31 with the highest amp hour rating and no (or lowest) CCA rating. Anyone know of this Duracell animal’s p/n from Sam’s? And cost?

    I thought ‘golf cart’ batteries were mainly 6volt! Requiring two to get 12v (not an option for me).

    Sams has a flooded ‘Marine’ battery 665 CCA, 105 AH FOR $109
    https://www.samsclub.com/p/duracell-marine-battery-group-size-29hm/prod3590216?xid=plp_product_1_2

    Vs. the $180 AGM I listed before. https://www.samsclub.com/p/duracell-marine-battery-group-size-29hm/prod3590216?xid=plp_product_1_2

    Both of these Duracell’s list a 20amp hour rate of 105. I’m not clear which would perform with more amp hour time for my probably mostly less than e amp draw, occasionally 4 amps running propane heater fan plus LED lights and charging a phone. When I do need to charge from my generator via 30 amp independent charger, would the flooded battery regain ‘close to’ a similar SOC to the AGM? They always say AGM charges faster, they never say how MUCH faster! The handy bodsolar link above says only 1% - 2% faster. If it was 25%-50% faster, that ‘might’ be worth more $. But I don’t think a 40% premium ($109 vs $180).
     
    Last edited: Jan 22, 2020
  17. Econ

    Econ Well-Known Member

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    GreyFox, I have respected your knowledge of electrical and since you didn't criticize it must mean I am learning.<GG>

    Somewhere buried in my saved paperwork there is a charger that has a smart module. You can dial in the voltages for bulk, absorption, and float. There has been some criticism that 14.8 may be a tad high.

    A couple months ago we quit using the converter to charge the house battery and switch over to solar. The converter never got up to 14.4 when checked. The solar got up to 14.4 every sunny day. The battery now has higher CCA as measured by a local auto store. Also it doesn't seem to discharge as quickly sitting in the basement. Unfortunately the specific gravities were not permanently recorded as I plan to check them today to see if solar has helped them. 1 and 6 used to be weak.
     
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  18. Econ

    Econ Well-Known Member

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    But you have twice the amp capacity. Longer periods between charging. I have a CPAP that has to be fed and investigating ways not to babysit a charger. It's taking away from my hiking time.

    Trojan is supposed to have 12 VDC true deep cycle. The next time we go to town the plan is to stop by the largest Trojan distributor in the state and talk to them.
     
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  19. GreyFox

    GreyFox Well-Known Member

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    Here's a Trojan battery spec sheet for their SCS200, picked at random ...

    http://www.trojanbattery.com/pdf/datasheets/SCS200_Trojan_Data_Sheets.pdf

    Bulk charging voltage is spec'd at 14.82 volts along with the reminder that temperature compensation is critical. The typical trailer converter isn't capable of either, even many stand alone chargers aren't either, particularly temp compensation. The decision as to which battery to buy shouldn't be based on just the battery but also the charging system one intends to use to maintain that battery. I'd speculate that the vast majority of RV owners don't pay attention to either, just buy what is available and cheap, and blindly destroy that battery prematurely by ignoring these important issues. Check out other Trojan batteries here and you'll see specifications for each battery they offer ...

    https://www.trojanbattery.com/

    ... buy a different brand and you'll have a different set of specifications. Here's East Penn's battery offerings ...

    http://www.eastpenncanada.com/

    For anyone interested here's a East Penn technical manual that explores the vagaries of their own brand of AGM and GEL batteries.

    http://www.eastpenn-deka.com/assets/base/0139.pdf
     
    Last edited: Jan 22, 2020
  20. Econ

    Econ Well-Known Member

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    I'll speculate that there are those who aren't fighting a CPAP who take the attitude that if they could improve battery life by 40% that's "only $40.00 US" on a Walmart special.
     

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