Quick question

  • Car is 10% dead, puled the battery out without it sparking and it's reading 6.5Volts, charger says it's charged.

    Should it read 12V ?

  • yes mate you should have 12v at the battery
    and a bit more like 13-14v with the engine & alt running.

    has the battery run dead flat then? 'might have gone past its best?!

  • new last year, but I left the lights on didn't I.

    It's on charge now 12V slow charge over night should sort it out.

  • thats normal for chargers to register a proper discharged battery as full, some chargers are able to charge 6v and 12v, if the battery is at 6.5v like you say then the charger will assume its a 6volt battery, and with it showing 6.5v it thinks its fully charged, youll need to force trickle the juice back in until you can get to around, 9-10v before itll start seeing it as a 12v battery and acting accordingly

  • Got ya, thanks guys, it's been on charge all night on a slow trickle charge, will leave it there for a few more hours then get the old meter out again.

    It just shocked me that a discharged battery was reading 6.5V, I know a car battery is 12V but that just made me go..huh?

  • copied…

    Every time a battery is
    discharged, its sulfuric-acid solution is gradually broken down, leaving
    deposits on the battery's lead plates. If the battery is promptly
    recharged, most of this sulphation is driven back into solution, leaving
    the plates in an essentially unchanged state. Leaving the battery in a
    discharged state for extended periods, however, allows the sulphation to
    harden into a form that permanently embeds itself within the plates.

    Suplhation deposits permanently reduce the battery's storage capacity.
    Chronic undercharging or excessive discharge also lead to plate
    shedding, in which some of the active solid-plate material flakes off
    and accumulates in the bottom of the battery. This accumulation
    eventually sorts out the plates, resulting in a dead cell. Consequently,
    if full storage capacity over a long service life is to be realized, it
    is important to fully recharge a battery promptly and to avoid over-

    Figure 1 - Battery State of Charge
    Charge Voltage Voltage Specific
    Level (12v) (6v) Gravity

    100% 12.7 6.3 1.265
    75% 12.4 6.2 1.225
    50% 12.2 6.1 1.190
    25% 12.0 6.0 1.155
    0% 11.9 6.0 1.120

    I think your battery might have been on its way out anyway, cos leaving just the side lights and rear lights on for 24hrs shouldnt be enough to do much. Each of those bulbs is only 5w, so 4x5=20 20w/12v=1.6amps. So on your average 60ah battery you should get 37.5hours before it was dead. What brand did you go for? Just out of curiosity, as I got a Yuasa on my bike, paid over the odds for it cos theyre regarded highly, and its utter rubbish, had to recharge it several times last year, the one I had before was one with a guys name on it, only remember 'Rob' being part of the name, and that never went wrong in 3 years.

  • it was a halfords own brand <6 months old.

  • most batteries come with a 1 year warranty, take it back and say that its not holding charge. Take a multimeter and show them its poor voltage output and explain that the plates have likely collapsed, causing the cells to merge and provide a low voltage, youll baffle them with knowledge even if you make it up and they should end up replacing it. Hell, if yu just said that the battery started meowing like a cat theyd probably accept that, they dunno what theyre talking about ever so youll be fine.


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