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Battery shows full charge, yet it's empty

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  • 24-06-2007 6:33pm
    #1
    peasant
    Registered Users Posts: 17,819 ✭✭✭✭


    How can that be?

    The main batt on my camper shows a full charge of 13.2V when you check it on the metre, but as soon as you put a load on it (switching on the lights is enough) all charge disappears into nowhere.

    I've checked everything else (no bad earth, alternator works, etc, etc) ..the battery has definetly had it and is going to get replaced (still under warranty)

    Just wanted to know how it could read fully charged when in fact all it's able to power is the radio (just about:D )


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    #2
    StephenC_IRL
    Closed Accounts Posts: 438 ✭✭StephenC_IRL


    the voltage may be there but the current mighent be, test the current and see what it says, also remove the caps off the battery and top up the water


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    #3
    peasant
    Registered Users Posts: 17,819 ✭✭✭✭peasant


    Havent' got anything to measure current ..but yeah ...there definetly isn't any. Battery is almost new (hence it's going back under warranty) and shows no obvious signs of malfunction, all cells are full of water.


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    #4
    bushy...
    Closed Accounts Posts: 1,467 ✭✭✭bushy...


    It could be sulphation , a layer of inactive crap builds up on the plates reducing its working ability to next to nothing. Some chargers are able to break it down if its not too bad or you can add a chemical to it ( edta i think) .
    Something like an Optimate charger ( ask in the 'bike forum) should keep the battery in top shape if the camper is sitting around a bit.


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    #5
    Alun
    Registered Users Posts: 21,464 ✭✭✭✭Alun


    When batteries go bad their internal resistance increases dramatically, therefore limiting the maximum current you can draw from them.


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    #6
    peasant
    Registered Users Posts: 17,819 ✭✭✭✭peasant


    The battery didn't hold a charge very long right from the beginning, but as I have built in charger on the van, I didn't worry about it too much. Just kept it charging when it was parked, assuming that things would right themselves over time.

    Was away last night and only for the fact that suspected things might go pearshaped and parked slightly downhill, did I get home at all. Otherwise I'd still be sitting in middle of nowhere in Donegal and the van dead as a Dodo.

    Bump-starting a big fecker of a Motorhome if all you have is some 20 meters of a very slight slope is a bit of an unnerving experiment ...but it worked :D


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    #7
    gyppo
    Registered Users Posts: 1,648 ✭✭✭gyppo


    Checking a battery by using a meter to check its voltage level will not tell you if the battery can supply a load. All meters on voltage settings have a very hig input resistance to avoid loading a circuit - so, while a battery appears to look ok voltage wise using a meter, as soon as a load is applied, the battery collapses.
    As Alun said, when batteries go west, its due to the internal resistance of the battery going high.
    Its quite possible the battery has been sitting around for a long time - it might look in new condition, but be past it. Is there a date of manufacture on it? Either way, I'd bring it back.


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