Dumb question on batteries
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  1. #1
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    Default Dumb question on batteries

    Hi

    This is a real dumb question and i should know better but my 205 will not start due to a flat battery, I have have tried to charge it but it will not charge up. Its been flat for about 4 months.

    I have tried to jump start the car with the battery in it but it will not start (does turn over though but not real fast).

    Would a dead battery in the car stop the car from jump starting? And could a battery just not be able to be recharged if left for a long time?

    the car was working fine before the battery went flat.

    cheers

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    A battery that has been left dead flat for months will have its life seriously shortened. I once jump started a car in this condition but as soon as I removed the leads the car stopped. The battery was that flat. An automatic charger recognised it as dead and would not charge it. I finally got some life into it by charging it in parallel with a good battery but it didn't last long.
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    1000+ Posts Andrew Ch's Avatar
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    Simple answer.....new battery time : )

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    so a dead battery would prevent a car starting via a jumpstart?

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    Quote Originally Posted by fluery View Post
    so a dead battery would prevent a car starting via a jumpstart?
    remember flu the only reason to jump start a car is to get the engine moving thus slowly recharging the battery(then you leave the car idling with jumper leads still in for about 5mins b4 driving off), as previously stated if the battery has been dead for some time its life will be drastically reduced.

    for the engine to start and work, it will need a steady feed of current for which your long dead battery will not give. so it will not work, just turn over a few times as you already said and even if you manage to charge it (in parallel) a bit it will die again shortly after.

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    but jump starting it does not get it running, it turns over but doesnt fire up and run. I would have thought that jump starting a car with a dead battery would get it running regardless and of course it might die again. what concerns me is that it wont start from a jump start,

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    Was the car you where jump starting off running ? Do have it running as this bumps the voltage up to 14.2V or something....

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    Quote Originally Posted by sfrawley View Post
    A battery that has been left dead flat for months will have its life seriously shortened. I once jump started a car in this condition but as soon as I removed the leads the car stopped. The battery was that flat. An automatic charger recognised it as dead and would not charge it. I finally got some life into it by charging it in parallel with a good battery but it didn't last long.
    Charging batteries is all about internal resistance.

    A stuffed battery has a very high internal resistance. Hence when you put it on charge there is next to no current flowing, ie "charge"

    A second battery in parallel will lower the combined internal resistance and allow the charger to deliver some current. This increases the terminal voltage on the crook battery. The good battery will charge the most but when that is fully charged the crook battery will try to charge.

    Left long enough the crook battery will charge to a degree, but because it is stuffed won't hold the charge. As soon as decent current is drawn it will die.

    In short new battery time

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    What amperage are the jumper cables that you're using?

    We had a similar problem with my girlfriend's car recently, a dodgy battery got installed which went completely dead overnight.

    I tried to jump start her car using mine with no luck. But we called the RAC and they jump started it no problem.

    I was curious and asked the mechanic why it hadn't worked trying the jump from my car. He told me that the cables I was using couldn't carry the required amperage to start the car from a completely dead battery, whereas the heavy duty cables the RAC used could.

    Could be your cables?

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    Quote Originally Posted by blink View Post
    Was the car you where jump starting off running ? Do have it running as this bumps the voltage up to 14.2V or something....
    Yes it was running. I guess the old battery is so dead it isnt passing on enough charge via the running car to fire up the ignition system, just enough to turn the engine over.

    thanks for the responses, it is time for new battery (i hope)

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    Quote Originally Posted by abe View Post
    What amperage are the jumper cables that you're using?

    We had a similar problem with my girlfriend's car recently, a dodgy battery got installed which went completely dead overnight.

    I tried to jump start her car using mine with no luck. But we called the RAC and they jump started it no problem.

    I was curious and asked the mechanic why it hadn't worked trying the jump from my car. He told me that the cables I was using couldn't carry the required amperage to start the car from a completely dead battery, whereas the heavy duty cables the RAC used could.

    Could be your cables?
    it could be the cables they are cheap and nasty ones maybe they are no passing on enough current. I might get the NRMA out and see if they can jump start it, at least they can sell me a new battery at the same time.

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    talk about missing the point

    to jump start the car do not connect the leads to the dead battery

    put the red lead on the positive post sure but the black lead needs to go onto a good earth on the engine not on the battery otherwise all you are doing is trying to put charge from the live car into a dead battery

    the car will start believe me with a dead battery

    the only reason a car will not run after you take the jumpers off is because the alternator is not working

    if the alternator is working there will be enough current to run the car

    a car will run without a battery

    when you get the car running listen for a whine from the alternator, this is a clear indicator that it is working, give the engine a quick rev as this will put the alternator into a state where it has some speed in order to kick it into gear so to speak

    this happens more often than not on a lot of cars that have sat for long periods of time

    let me know how you get on with it
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    Sorry to digress a little.

    Before you go the new battery route check that the battery terminals make good contact with the posts and that whatever device is used to clamp the cable to the terminal it is doing its job. Also check that the positive to starter motor terminal is tight (if you need to tighten it, remember to disconnect the battery otherwise your spanner will get really hot...).

    Depending on how you attach the jumper cable clamps, poor terminal connection could have some influence being able to start the car.
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    You said the battery has been dead for four months. How old is the fuel in the tank of the car? Stale fuel can make starting difficult.

    a can of start ya bastard might be necessary to get it running. I used to find with my morris when it had been sitting for months without being started it was a pain to get going (but start ya bastard would get it going quick time) after running it for a while it would then start without problems. Could be that the fuel in the carbie was more stale than the rest and getting it running for a while got less stale fuel from the tank...

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    It's also important to remember that a lead-acid battery is fully discharged at 1.72V per cell (10.5V) and irreversible sulphation starts to occur. So keep your battery charged if you want it to last. A fully charged battery is 2.3V per cell (13.8V).

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    Here's what you should now do... remove your battery and replace with a battery that you know is charged.

    If the car starts then take your old battery to auto elec to test. Make a decision based on result.

    If the car won't start look for other possible causes......

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    Quote Originally Posted by pugrambo View Post
    t
    to jump start the car do not connect the leads to the dead battery

    put the red lead on the positive post sure but the black lead needs to go onto a good earth on the engine not on the battery otherwise all you are doing is trying to put charge from the live car into a dead battery
    it
    i know this is not addressing the OP's issue, but there is no difference between putting the jumper cable on the battery terminal vs a good earth anywhere on the car. they are electrically the same. for it to make a difference it would require some significant resistance between the car body/motor, and the negative terminal on the battery. that is not the case!

    i have had people say it is to avoid sparks near the battery and therefore explosion risk - as if the +ve cable on the other terminal wouldnt do that.

    that aside, if you cant charge your battery (i presume you mean on a battery charger, then it IS stuffed, so just buy a new one without a second thought. even if something else is up, you still need a new battery. experience suggests that if you think they might be rooted, they are, and there is nothing for it but to just get a new one.
    Last edited by alexander; 11th April 2012 at 10:45 AM.

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    Quote Originally Posted by alexander View Post
    i know this is not addressing the OP's issue, but there is no difference between putting the jumper cable on the battery terminal vs a good earth anywhere on the car. they are electrically the same. for it to make a difference it would require some significant resistance between the car body/motor, and the negative terminal on the battery. that is not the case!

    i have had people say it is to avoid sparks near the battery and therefore explosion risk - as if the +ve cable on the other terminal wouldnt do that.

    that aside, if you cant charge your battery (i presume you mean on a battery charger, then it IS stuffed, so just buy a new one without a second thought. even if something else is up, you still need a new battery. experience suggests that if you think they might be rooted, they are, and there is nothing for it but to just get a new one.
    sorry alexander it makes a big difference

    the dead battery will be a sponge for any incoming current

    my years of experience is something i will back on this each and every time

    by placing the earth directly on the engine you have a much better current flow from the donor car/battery, even better if you can put the positive lead directly to the starter but this can be near impossible in most cases so the pos terminal on the battery is the only option
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    if that is true, then you need new battery cables, 'cause that aint how it works.

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    Icon14 I agree Pugrambo...

    Quote Originally Posted by pugrambo View Post
    sorry alexander it makes a big difference

    the dead battery will be a sponge for any incoming current

    my years of experience is something i will back on this each and every time

    by placing the earth directly on the engine you have a much better current flow from the donor car/battery, even better if you can put the positive lead directly to the starter but this can be near impossible in most cases so the pos terminal on the battery is the only option
    I agree with what you say PR and I would not worry too much about stale fuel over 4 months. I was trying to start a Commodore at the weekend that hadn't been running for five years - main problem was getting the fuel through the mechanical petrol pump, in the end I had to prime the pump itself and once the fuel started to come through to the carby, refitted the hose to the tank and it idled quite nicely on the old stale petrol.

    Also be aware that the new style batteries need a different staged charger to put life back into them after going flat. I'm using a 7 stage automatic Projecta 12 volt 8000 ma charger which has a manual recondition function and staged amperage 2am, 4amp, 6amp, and 8amp. which seems to bring such batteries back to useful life. I thank the Aussie froggers who put me on to that unit, it's saved a few batteries.

    Ken

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    Quote Originally Posted by alexander View Post
    if that is true, then you need new battery cables, 'cause that aint how it works.
    sorry alexander

    on this one i will stand toe to toe with you and tell you that you're wrong and i am right

    as i said, i'll back all my years of experience on this every single time

    you will never see an experienced roadside repair bloke do it your way either, they will always stick the earth on the engine not the battery

    i don't care how you want to try and talk your way around this one but by putting the earth on the engine is always going to throw more current into starting the dead car than sticking it on the battery, it's FACT
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