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Thread: Battery Voltage

  1. #1
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    Default Battery Voltage

    Last Sunday the battery on my Moto Guzzi 1000SP is at (measured with a voltmetre) 12.41.
    Indicator says "battery OK".
    Bike starts immediately, and starts again without hesitation several times during the day.
    At the end of the motorcycling day I measure the voltage: 12.80. I start the bike in the garage three times to see if it gets tired, it starts every time without hesitation. I measure the voltage again: even higher at 12.88.

    Fast forward to this afternoon, seven days later.
    Voltmetre reading is 12.48, higher than one week ago. However, this time the battery does not manage to start the engine. I need to jump start the bike and, after that, everything is fine all afternoon.

    What's going on? If the battery is at the end of its useful life it should not have read as high as 12.48 this afternoon, after a week of inactivity, right? How can it be that bike started without hesitation with the voltage at 12.41 last week, and did not start with voltage at 12.48 today?

    The cables were checked and, again, the battery worked a treat all day after the jump start, so it wasn't that.

    Can anyone explain?

    Thanks

    O

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    Should Get Out More TheEnglishman's Avatar
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    Default Re: Battery Voltage

    A battery's ability to power a starter motor isnít defined by its voltage output but by its ability to deliver current. A lot of current. Try a smart battery charger/conditioner. And the terminals on the battery are clean and tight. Same with the starter motor.

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    Default Re: Battery Voltage

    Many knackered batteries can be charged to a normal voltage, but that voltage drops too much when a load is applied, because the battery has lost capacity.

    Next time your battery is charged up, try switching the headlight on (engine off) and seeing if the voltage drops much over the next 10 minutes.

    Or- bike workshops can test it.

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    Default Re: Battery Voltage

    Why were you repeatedly checking the battery in first place? Had you already problems with it?

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    Default Re: Battery Voltage

    12.48 is effectively flat, and as said you need current to start it. New battery time I would suggest.

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    Should Get Out More Kneerly Down's Avatar
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    Default Re: Battery Voltage

    For an undamaged lead acid battery 12.48V would normally indicate 75%+ state of charge (it depends on temperature and other factors)...well above 50% and certainly not 'flat'.

    It could well be that this battery has internal issues that leave it unable to deliver sufficient current for the starter though.

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    Default Re: Battery Voltage

    Thanks all.

    Battery is (was) an excellent, brutally powerful Motobatt MBTX30UHD battery I liked a lot, bought last year.

    Unfortunately, as I gave my bike to the paint shop for a new paint I forgot to disconnect one cable; when the bike was given back to me - actually a couple of months later - the battery was dead.
    I have one of those chargers-conditioners, and put it to work on the battery. It took days, but then it said it was fine and the battery was "saved" (it tells you if the battery cannot be reconditioned). Bike started immediately etc. However, three weeks of inactivity (I was away on holiday with the other bike at the end of April) left it empty (I mean really empty, not at all like yesterday. I heard that tac-tact-tac-tac noise you get when there is no chance).
    However, once the battery is jump started it works quite fine.

    I was confused all the time because I thought that the voltage gives a clear indication of the health state of the battery, and my voltmeter said "fine". Also, once jump started it delivers several ignitions in a row, without missing a beat, first time and no hesitation (my Moto Guzzi 1000 SP needs a lot of "kick" to get started, so you start to notice when the battery is weak). Dead, it certainly ain't.

    I will certainly buy a new battery (identical) if needs be, but I am confused as to the fact that the battery seems actually fine most of the time and kicks like a mule after the initial kickstarting, with the voltmeter saying "your battery is fine".

    Would it make sense to try the "conditioning" again, or would you say it is time to order the new one?

    Thanks

    O

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    Should Get Out More Kneerly Down's Avatar
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    Default Re: Battery Voltage

    I've never had any luck trying to recover Motobatt or Odyssey batteries such that they are good enough to continue using on a heavy duty starter (in my case a R1100RT)
    Different experience with the batteries on the VFR750 over the years...I've owned both for just over 20 years so have had a few different batteries!

    Imagine your MG is more like the RT.

    Pretty sure most of the 'smart' battery chargers just look for voltage drift rather than doing anything like a proper load test.

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    Default Re: Battery Voltage

    I had a feeling the glass mat technology (or whatever those fancy batteries are) could be recovered from near full discharge. IIRC the manufacturers said you needed their special charger though.

    It's a tricky one.. has one on't cross beams gone awt askew on't treadle?

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    Default Re: Battery Voltage

    Quote Originally Posted by Kneerly Down View Post
    Pretty sure most of the 'smart' battery chargers just look for voltage drift rather than doing anything like a proper load test.
    The one I have (an Optimate) and all the others I have seen are far too weedy to o a proper load test.

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    Default Re: Battery Voltage

    In your estimation, is bringing the battery home and subjecting it to the same "conditioning process" again (my conditioner is also an Optimate) likely to yield appreciable results?
    I don't mind buying a new battery straight, but I would like to be sure that there are no reasonable alternatives before spending the £90...
    Thanks
    O

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    Default Re: Battery Voltage

    Take it to a battery shop and get it load tested.

    I still think if it loses that much charge in such a short time it's had it.

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    Default Re: Battery Voltage

    My experience is that the AGM batteries are great at holding charge for a long time but when they go they are gone.

    I had an Odyssey AGM battery for my R1100RT that I bought just before we moved up here.
    It got put in a box of keepsake stuff and went in the store room...for the next 10 years.
    When we found it I thought I'd put it on charge, just in case, and it's fine.

    A 3 year old Odyssey battery I had showed fine for voltage but neither the CTEK or Optimate managed to get it so it would actually deliver useful current though.

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    Default Re: Battery Voltage

    Thanks to all!
    I am resigned to the expense now (my fault anyway). I'll go for another Motobatt as the cranking power is just beautiful (suggested battery for big Harley Davidsons...)

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