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  1. #1
    bowsniper's Avatar
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    Interesting AGM numbers

    I took my battery to Advance auto parts to get it checked out

    it is rated at 325 cca and turned a number of 525! Wow... the meter said it was good and needed more charging . It had a voltage of 12.3
    I guess the .3 is what's left to charge. Total voltage should be 12.6 v.

    Anyone else get numbers like this? This battery was bought about a year ago.looks to be fine to me.

    PS. I know I spelled interesting wrong on the title.
    Damm ol eyeballs on a smart phone.lol
    Last edited by K447; 05-23-2013 at 09:06 AM. Reason: Interesting


  2. #2

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    I question the reading of 525 sounds too good even for a brand new battery.

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    What voltage indicates fully 100% charged for an AGM watercraft battery?

    Quote Originally Posted by bowsniper View Post
    I took my battery to Advance auto parts to get it checked out

    it is rated at 325 cca and turned a number of 525! Wow... the meter said it was good and needed more charging . It had a voltage of 12.3
    I guess the .3 is what's left to charge. Total voltage should be 12.6 v.

    Anyone else get numbers like this? This battery was bought about a year ago.looks to be fine to me.
    12.6 volts would be for non-AGM traditional lead-acid batteries.

    A fully charged and rested AGM battery should measure about 12.8 volts (or a little higher) depending somewhat on battery temperature. Going from memory, an AGM battery is fully discharged at 11.8 volts, and 12.3 volts would be about 50% charged.

    These voltage differences compared to regular lead-acid batteries is one of the reasons for needing 'AGM compatible' AC powered battery chargers, as non-AGM chargers don't get the voltages correct to provide accurate charging of AGM batteries. When installed in a running watercraft, the AGM battery gets along just fine with the stock charging system on the engine.

    See page 13 for the Deka AGM battery Voltage vs. State of Charge chart;
    http://www.dekabatteries.com/assets/base/0139.pdf

    Click image for larger version. 

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  5. #4
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    you need to reset your brain when dealing with AGM batteries..specially the part where you cannot tell what the state of the battery really is until 24 hours after it's come off the charger.

    I recently had to eat a Deka battery that somebody had used a conventional charger on. It read 12.8 volts at rest, showed a green light after 24 hours on my battery tender jr. but wouldn't push any amps to crank an engine.

    Sure enough when it was on the conventional charger, it overheated and vented..the vents are one way..when they open..that's it.

    I had another one fail on a Yamaha vx..turns out the voltage regulator was a bit out of spec and cooked the battery thru a series of minor overcharges.

    It was one of a pair, the other skis battery read full AGM charge and had no problems. The batteries were purchased by me at the same time.

    I ended up replacing the voltage regulator on the one that cooked the battery. The battery was two years old, but I discounted the replacement ( great customer)

    After discussing with Deka..future batteries may have a telltale when the vent blows open..one of the reasons they cut the warranty to 6 months is that they were getting way too many warranty claims for batteries that had been overcharged ( with a conventional charger)

    I'm looking at less then a 2% failure over the lifetime of all the DEKA batteries I've sold..all from overcharging. I've gone to zero tolerance on voltage regulators that are even .1v over spec on systems with an AGM battery due to this.

    btw, I've found on a few Yamaha 4 storkes that the console displays voltages .3 under actual measure with a quality voltmeter @ the battery

  6. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    On Polaris I never trust the digital dash display to be accurate with voltage. Rarely does the MFD/MFI agree with my digital multi-meters (several, mostly Fluke brand).

    I have not been worrying about over charging on stock engine charging systems, as long as the charging voltage wasn't stupidly out of spec. Perhaps I should be more picky about what charging voltage range with the engine running at various RPM is 'acceptable'

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    bowsniper's Avatar
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    I did use a. Convential charger on the lowest setting for 10 hours. Thx for the input. So, does this mean I have to use a AGM battery charger to get the 12.8? When charging or....will the ski provide the last lil.bit once running? I never had an issue with it so far.

  8. #7
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by bowsniper View Post
    I did use a. Convential charger on the lowest setting for 10 hours. Thx for the input. So, does this mean I have to use a AGM battery charger to get the 12.8? When charging or....will the ski provide the last lil.bit once running? I never had an issue with it so far.
    If the battery has enough power to start the engine, then the watercraft charging system should continue to charge the battery. The key is the ratio of run time to number of engine starts. Every engine start consumes some battery power. The charging systen then works to slowly restore the energy into the battery.

    The longer the engine runs, especially above idle RPM, the more the battery will charge. Many short runs with multiple engine stops, then restarts, will not recharge the battery very much.

    I have never had a concern, but I normally ride significant distances once I get it running. And of course I fully charge the batteries before the first ride of the season.

    Only when the ski has been sitting for many weeks do I bother to hook up the battery maintainer (AGM compatible, of course).

  9. #8
    bowsniper's Avatar
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    That's what I figure too. It should be fine. I'll have to look into a AGM charger. I can tell ya one thing...at the gathering last year, I had the intake hose fall off from the intake filter---the fitting got crushed and fell off somehow. Anyways....I used the battery to get the ski to shore. Turned over many times.shows the reserve po

    wer of an AGM battery.,

  10. #9
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    AGM chargers are far cheaper then new batteries..walmart has em for under $30.

    I prefer the slightly more expensive battery tenders myself.

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