A question about battery drain.

Discussion in 'General Motoring' started by Freewheeling, Jul 26, 2007.

  1. Freewheeling

    Freewheeling Guest

    I was in a small fender-bender in the parking lot a few days ago, that
    practically tore of the front fender. There was no fluid leakage,
    however, so I drove it home after going through the accident report
    formalities. (I have a 1998 SL2 4 door.) The next day I had a doctor's
    appointment so after duct taping the fender sort of back in place I
    tried to start the car, but the battery was completely dead. I mean,
    dead as a doornail.

    Now, it was raining fairly hard the night before and all that day and I
    figured that the rain must have shorted some exposed wiring. The shop
    did some testing that indicated there was no drain on the battery, so
    they concluded I must've left the light on or something. When I parked
    the car, however, after the accident, the sun was shining brightly so
    there'd have been no reason to turn on the light. Moreover, as I recall
    there's an automatic shut off if you turn off the key and leave the
    lights on. This mechanic tells me that isn't true, and that if you
    leave the lights on the battery will just drain. (All the doors were
    shut tight, by the way.)

    So, I'm thinking that:

    1. The fellow is wrong about the automatic shut off, because that's one
    of the features I liked about the car.

    2. If they didn't test the car "wet" then how would they know whether
    there was a drain on the battery system from exposed wiring that shorted
    due to water?

    What do you think? Am I on any solid ground here?

    --Scott
     
    Freewheeling, Jul 26, 2007
    #1
  2. Freewheeling

    Dooger Guest

    It's likely he's wrong. But that's a moot point.
    Did the battery charge up and work OK after you found it wouldn't start
    the car?

    My thought on the exposed wiring...

    There should be no current to those wires to "short out" whether wet or
    not. The switch inside controls when there is current to the wiring for
    the lights and that may work through a relay which will certainly be
    inside the engine compartment or another secure place.

    I'd be looking for some other source for the problem.

    Best, wes
     
    Dooger, Jul 30, 2007
    #2
  3. Freewheeling

    Freewheeling Guest

    Wes:

    Thanks. The battery charged, or at least it charged enough that I could
    turn the key off and then restart. I'm virtually certain I didn't leave
    the lights on, and the doors were shut tight and locked. I have
    noticed, in the past, that sometimes the key wouldn't turn over the
    motor, so I'd leave the car in gear and rock it a little, then take it
    out of gear and the ignition worked fine. But there was no battery
    drain. The ignition switch was just finicky, and they checked the
    alternator anyway as part of their diagnostics.

    Frankly, that's the least of my problems at this point. But I was
    curious why the battery might drain after a collision. If they checked
    for, and couldn't find, a drain on the battery then the rain must've had
    something to do with it. Either that, or I'm mistaken about the lights
    being on. But if there's a timed shut-off switch for the lights then
    that leaves some rain-related/collision-related problem, or at least
    rain-related/something-related, so the question about the shut-off
    switch wasn't quite moot.
     
    Freewheeling, Jul 31, 2007
    #3
  4. Freewheeling

    BläBlä Guest

    Parasitic draw test and Load test. Not much else you can check for at
    this point.
     
    BläBlä, Aug 1, 2007
    #4
  5. Freewheeling

    Dooger Guest

    Assuming the rain has stopped...maybe whatever else may have caused the
    battery to drain stopped for a while too. I'm sorry but the chances that
    rain caused your battery problem is slim to nil...and slim just bought a
    ticket out of town. Do this sometime...take a charged up battery and hook
    wires to each post and then lay the other ends in a puddle of rain water
    overnight.

    You already said the battery/starting system has been flaky in the past.
    That's where I'd look first.
    Things are not always either/or.
    Not necessarily.

    Sure it was. If the wires aren't energized they can't "short" out. And
    rain water isn't going to cause enough current to pass between bared wires
    or "something" to affect the battery much one way or the other. So unless
    you left the lights on and there wasn't a safety shutoff switch there
    could have been no "short" in the wires. Distilled water is a very poor
    conductor and rain is pretty much distilled water.

    Best, wes
     
    Dooger, Aug 1, 2007
    #5
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