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how to charge a 12V, 44Ah car battery with trickle charger ?

Discussion in 'Power Electronics' started by flabbergasted, Oct 10, 2011.

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  1. flabbergasted


    Oct 3, 2011
    Hi, I want to charge a 12V, 44Ah car battery to keep as a spare battery in the trunk of my car. I used it to start my car twice but it doesn't have enough juice to turn over the engine anymore. I am trying to charge it with a 12V trickle charger, on the charger it says 12V, 1500mA, it's been connected to the battery for 2 hours so far and the green light that signals the battery is charged has not come on yet.

    Will this charger (12V, 1500mA) charge the battery (12V, 44Ah, 18VA max) ?

  2. BobK


    Jan 5, 2010
    It would take 44 / 1.5 = 29 hours to fully charge an empty battery if it were 100% efficient. I believe charging is somewhere around 60% efficient, so, about 29 / .6 = 48 hours. 2 hoiurs ain't gonna do it.

    Good luck.

  3. duke37


    Jan 9, 2011
    VA is a term used for AC circuits, how does this apply to a battery?

    If the charger is charging at 1A and the battery is discharged, the battery therefore needs 44Ah, you need to charge for 44 hours minimum.

    Having a loose lead/acid battery in a car gives me the collywobles. Have you thought about what would happen in an accident. A shorted battery could start a fire and if split would spray sulphuric acid over the car causing corrosion if you are lucky and over you if you are unlucky.

    A battery self discharges and needs to be topped up at least once a month to stop sulphation and loss of capacity.

    Why not get the car electrics mended?
  4. flabbergasted


    Oct 3, 2011
    Oh sorry that is from the charger.

    Thanks for the info duke37 and BobK, the battery charged in 8 hours, i guess it wasn't totally flat.
    duke37 you have a very good point about keeping a spare battery in the trunk, i will think about that and maybe just buy a new battery.

    Last edited: Oct 11, 2011
  5. davenn

    davenn Moderator

    Sep 5, 2009
    failing all that, why not just do the obvious....
    Charge it off the existing car charging system thereby having a fully charged battery available ALL the time ?
    batteries rolling around in trunks ... naaa not a prob. there are many ways to secure them!! its something us ham radio
    operators do often for additional power when up on hilltops doing comms stuff :)

  6. Resqueline


    Jul 31, 2009
    If it reached "full charge" in 8 hours with a 1.5A charger then the battery presently holds no more than 12Ah. It is probably seriously sulphated and needs more charging.
    I recently drained my own starting battery completely (by leaving lights on) and while it seemed to be recharged within 24 hours it needed a week to regain full acid density.
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