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Testing deep cycle battery capacity

Discussion in 'Newport' started by MitchK, Dec 26, 2017. Add this thread to a FAQ

  1. MitchK

    MitchK

    Joined Sep 22, 2017
    42 posts, 5 likes
    Capital Yachts Newport 28
    US Burbank, Wa Burbank, WA
    Hi all,
    Got another question in regards to batteries for this learned group. As I have posted before, I have a set of optima blue top 34M batteries in the Newport 28-2 I picked up a few months ago. In looking through the very limited log book that came with the boat, I found an entry that stated one of the batteries had been replaced in 2011. So I have been concerned with the current condition of the batteries. I was just going to replace them with another set of blue tops, but after seeing the prices, I decided I better see just what condition the existing batteries were in before I made a decission. I already had a load tester, and used it on the batteries. Both batteries passed, not real high on the scale, but they did pass. Now knowing that deep cycle batteries are designed for a much lower discharge rate, I figured I better test the batteries at a lower discharge rate. I do not have a constant current load, so the best I could come up with is a constant wattage load. Not perfect by any means, but it would at least give me a general idea of the batteries condition. I took a small inverter, and a 50 watt light bulb and hooked it up to each battery, turned it on, and let it run. The load was a little high at approx. 4 Amps, but close enough for what I wanted. The first battery (no date sticker on it) didn't fair too well. After approx. 12 hrs, it had dropped the battery voltage to 10.4 volts. At this time I stopped the test. On the newer battery ( date sticker of 2011) I performed the same test. After the same 12hr test, the battery voltage was still at 11.5V. So with all of that said, it looks like I still have some life left in the newer of the two batteries, and the older battery will definitely have to be replaced.

    The interesting thing about these batteries, is they sat in some level of discharge for long periods of time. As best I can tell, the boat had not been out of the slip more than about 25 times in the last 10 years, and the boat was not connected to shore power, does not have a battery charger on board, nor does it have any solar. I will be installing a Pro Mariner Pro Sport 20A charger to keep the batteries charged between uses. This particular charger has a setting specifically for AGM batteries.

    The Optima batteries are nice in that they are spill proof, they do not normally off gas, and they seem to have a pretty long life. But they are expensive. The best price I have been able to find is over. $200.00 each. Well over twice the price of a normal wet cell battery.

    Well, that about sums it up on the battery issue. Guess I now have to make a decision as to what type of battery I want to put back in the boat.

    Mitch
     


  2. jeepbluetj

    jeepbluetj

    Joined Jan 18, 2016
    377 posts, 91 likes
    Catalina 30
    US SoCal Dana Point
    The optima batteries offer absolutely no advantage to a boater that I can figure out. They have less capacity for their size than more conventional AGMs or FLAs. They're very expensive. The only thing an optima excels at is ruggedness - you can shock them quite a bit more than other batteries - particularly FLAs. I've used the optimas in my jeeps quite a bit - they last 5-6 years where a FLA would last between 1 week to somewhere less than a year. But you're most likely not driving your boat on rocks the size of volkswagens, and umm.... yea, I do that sometimes with the jeep.

    If you like the spill-proof nature, look at conventional AGMs. You won't save any $$$, but you'll get a battery better suited for the use. Me? I really like FLAs. 6v GC2s to be precise. They're cheap, readily available, have plenty of capacity, and take quite a bit of abuse. You need them in pairs because they're 6v. I've no idea if they'd fit your boat.. AGMs do not like to be abused (Undercharged, PSOC, etc....) FLAs don't like to be abused either, but they are better and handling it and they're a whole lot cheaper. For the folks that are gonna kill a set of batteries every three years, may as well spend $200 instead of $600.

    Read Mainesail's musings on batteries for more info. Found a linky that goes into AGMs pretty well: https://forums.sailboatowners.com/index.php?threads/agm-batteries-making-the-choice.124973/
     


  3. Maine Sail

    Maine Sail Moderator

    Joined Feb 6, 1998
    10,431 posts, 354 likes
    Canadian Sailcraft 36T
    US Casco Bay, ME
    Mitch,

    The original Optima batteries were a very high quality product and the technology was invented by EnerSys. EnerSys builds premium batteries for the military/defense sector, aerospace, banking, industrial, & the medical/pharmaceutical sectors among others. We get to benefit from their quality in the consumer divisions which use the same technology.

    EnerSys sold the Optima product off to JCI (Johnson Controls) because they replaced it with TPPL (thin plate pure lead) flat plate batteries that yield better Ah capacity & cranking in the same foot print.

    Since JCI bought the product I have not had good luck with the Optima batteries. I used to use them for some starting applications but no longer do. I never used them as house banks because the Ah to cost/$$$ ratio is quite poor.

    The Ah's to $$$ hit with Optima batteries is simply due to the cylindrical cells wasting space and not utilizing the entire foot print of the battery for capacity & lead. Cylindrical cells simply don't allow as much Ah capacity in the same foot print as a flat plate battery does. For example the Odyssey 34M has a 20 hour capacity of 68Ah or 13 more Ah's in the same physical foot print than the Optima 34M.

    Your test should run at 2.75A or 55Ah/20h = 2.75A
    The battery should ideally be between 72F and 80F
    Keep the load as close to 2.75A as possible
    The battery should run for at least 16 hours (80% of rated capacity) before the terminal voltage falls to 10.499V
    For coastal cruising a battery like that can still be used down to about 70% to 75% of rated capacity before they begin to get unpredictable. It seems like you have one battery that is still worth keeping. Maybe devote it to starting purposes and replace the house bank..
     


  4. MitchK

    MitchK

    Joined Sep 22, 2017
    42 posts, 5 likes
    Capital Yachts Newport 28
    US Burbank, Wa Burbank, WA
    Maine Sail, jeepbluetj,
    Thanks for the reply(s). I am aware that the coiled cells have less capacity that a standard flat plate. The tests I ran were just for comparison sake to get an idea of the condition of the Optimas I currently have. I knew the load was a bit higher than it should be for the 20hr test, but I did not have a lower wattage incandescent bulb to use at the time. I figured 4A was close enough for what I needed to know. As it stands, the older battery needs to be replaced. The 2011 dated battery still has some useful life in it. The tests provided the info I needed. I will be replacing both batteries when I do as the charger I have (ProMariner Pro Sport 20A) to keep them topped up between uses is a three stage intelligent (supposedly) and both batteries need to be the same "type". I can select between Flooded/AGM, Gell, or HP AGM (Optimas. etc).

    I am located on an inland river, so not as critical as say an open ocean cruising yacht, but I do like things to be as reliable as I can make them.

    I do like the convenience, low maintenance, and relatively long life that the Optimas seem to be capable of. I had looked at the Odyssey's, but the price per amp is a bit steep, even more so than the Optimas. From my limited web searches, it looks like Odyssey's are a bit more expensive than the Optimas. So with the price difference, even with the additional capacity, they are not really cost effective either.

    At this time, it looks like I will be going with a pair of Group 24 flooded cells if for no other reason, cost and capacity.

    Actually the biggest reason is I will not be able to treat the AGM's the way they need to be treated, so I would be wasting money on the AGM's
    -The M-18 has the factory dumb alternator, that I do not want to replace at this time. I think the max output is around 35A.
    -I do not currently have solar, however, it is planned for a limited solar system for maintaining the batteries. Probably no more than 50 watts capacity.
    -No plans for a wind generator.
    -I do not want to modify the existing battery compartment to allow installation of larger batteries, So I am limited to what will fit the existing battery box. It looks like the largerst that will fit are 34M's AGM's. The Group 24's have the same foot print, but are a couple of inches taller for more plate area.
    -The boat will be used mainly for weekend trips. Usually no more than a couple of days at a time. For longer trips, I will have to figure out some way to bulk charge the batteries without having to run the engine. Maybe upgrade the solar.

    Fortunately, the cranking Amps of the little Universal M18 diesel is not that high, and it starts easily, so should not be too much punishment for the flooded deep cycle batteries. I usually turn the battery switch to Both when starting, then after a short while, switch back to the house battery for the normal loads. At least that is the way I have been doing it since I got the boat a few months ago.

    Again, thanks for the replies.

    Mitch
     


    Last edited: Dec 29, 2017
  5. jeepbluetj

    jeepbluetj

    Joined Jan 18, 2016
    377 posts, 91 likes
    Catalina 30
    US SoCal Dana Point
    Read Maine's treatise on 1/2/both switches.

    If you can find room to keep the 'good' optima (since it doesn't need to be in a battery box) - you could use that as your 'spare' battery - then wire up the other batteries as a single bank. Use the new batteries for starting and house, i.e "main" and "spare" banks. The only thing the old optima is for is the unlikely event you kill the "main" bank so you can start your engine.

    That's how I run my boat - I do everything off the "main" bank and have a small spare battery. I could likely get rid of the spare battery and just have a portable jumpstarter thing.
     


  6. Maine Sail

    Maine Sail Moderator

    Joined Feb 6, 1998
    10,431 posts, 354 likes
    Canadian Sailcraft 36T
    US Casco Bay, ME
    The cost of the battery can not be measured in just Ah's per $$ the equation is Ah's per dollar / expected cycles. In this case the Odyssey kills the current "cheapened" Optima's. I used to easily see 5-7 years+ out of Optima stating batteries and I now see 2-3 years and this is without any cycling. You can't compare the price of a cheap battery riding on its well earned reputation vs. a true premium AGM. it is like comparing the cost per Ah of an East Penn AGM to a Northstar, Firefly, Lifeline or Odyssey.. [/quote]




    Good choice.

    In that range the best of the lot are the; US Battery US24-DCXC, the Trojan SCS150 & the Crown 24T-1000. Interestingly enough these three are the only Group 24, 27 & 31 brands I've tested that have actually been able to deliver their rated rated Ah capacity or darn close (within 1Ah).

    An entire article I was working on for PS was scrapped after well over 400 hours of testing because the vast majority of flooded "deep cycle" G-24, 27 & 31 batteries could not deliver their rated capacity no matter what was tried. Only three brands we tested could actually meet their stated claims on Ah capacity or within 1Ah... Caveat emptor.......
     


  7. MitchK

    MitchK

    Joined Sep 22, 2017
    42 posts, 5 likes
    Capital Yachts Newport 28
    US Burbank, Wa Burbank, WA
    Had a chinook wind come through last night and today, which melted most of the snow and ice we got over Christmas, so I was able to get aboard the boat and reinstall the one good Optima in the boat today, and removed the two group 27's I had temporarily installed a couple of months ago. I also installed a 5 watt solar panel that is direct wired and fused at the battery. Hopefully with no loads turned on, it will be able to keep the Optima topped off until spring. Now the search begins for a local distributor of a good grade of flooded cell. My wife recommends going ahead and spending the money for good AGM's (Odyssey, etc). I explained we really did not have the necessary electrical configuration to make it worth while to spend the money for more expensive batteries. Maybe the AGM's would last longer than the flooded cells. I do not believe they would, or at least not long enough to justify the extra expense. I do plan on adding a more substantial solar panel, just need to figure out where to mount it. I am figuring with such a small battery system, a 50 watt panel will be plenty to keep the batteries fully charged between uses. In the future, if we get the opportunity to spend longer periods of time on the boat, I will consider at a larger system.

    Another question, do I need to put each of the batteries in a separate battery box? The boat has a molded in recessed battery tray that holds two batteries. The tray is at least 2" deep, so I have a fair amount of spill over capacity. At this point, I am considering purchasing two group 24 battery boxes, and installing them along with the new batteries.

    And, before I forget, Happy New Year to all.

    Mitch
     



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