Battery or Alternator.

[KieranEbbett2500]

Hi all. Today my car would not start, had a flat battery. So jump started it. But once I'd driven to work about 40kms, at idle it had about 12.5 on volts gauge. The battery and regulator and brushes in alternator are less then 8 months old. There has been a problem with battery acid build up.

Any help would be appreciated greatly

[tony]

Can you get a voltmeter, disconnect the negative battery terminal, and put voltmeter between battery terminal and earth with the key turned off and see if anything is draining the battery. I wouldn't trust the accuracy of the car's voltmeter.
Don't quite understand "battery acid build up"
Tony.

[tony]

Can you get a voltmeter, disconnect the negative battery terminal, and put voltmeter between battery terminal and earth with the key turned off and see if anything is draining the battery. I wouldn't trust the accuracy of the voltmeter in the car.
Don't quite understand "battery acid build up"
Tony.

[Mike Stevens]

As Tony says, I wouldn't trust the accuracy of the dash voltmeter, except if it now reads lower than it did before. It does sound like a faulty alternator though.

Tony is suggesting that you try to measure the residual battery current when everything is turned off. You need to set the multimeter to current range to do this but do it with extreme caution. There is a lot of energy in the battery and you don't want this to be dissipated in the multmeter!

I would attempt it as follows -

Loosen the battery negative terminal but don't yet disconnect it.
Connect the multimeter with one side on the battery post and the other side on the earth somewhere.
Without disturbing the meter connections, now disconnect the battery negative terminal.
You can then measure the residual current.

The reason for all this palarva is that that will probably be some surge currents when you first connect the battery and you don't want that surge current going through the meter! The above method should help avoid that!

Cheers,
Mike.

[KieranEbbett2500]

Sorry for the delay.

Just to clarify first of all. By build up of acid I mean that the entire length of the battery clamp after a couple of weeks will be covered in white acidy residue.

Sadly I dont own a multimeter... so have not tried your suggestion. I did charge the battery overnight and so far it seems fine. But using lights, fan and wipers will show a noticeable drop on cars gauge. I'm having similar issues I'm my 1850 dolly. Turned the heater fan on and radio turned off.... I've wondered about up rating the alternator??? Thanks again!

[eckplant]

Sorry to hear of your battery woes...... regarding the battery terminal furring up/corroding, this can quickly develop even on a new battery if the clamp was dirty at the changeover, always make sure both terminal and clamp are spotless and TIGHT, and use some petroleum jelly, a good connection will also lead to good charging.
I noticed there was no mention of any added accessories, i.e. Alarm, CD player etc that could cause a parasitic drain, a good buy for your car is a battery isolator switch that has a low load fused bypass for a clock or whatever.
You can pick a multimeter up for under £7 from screwfix, when the car is running and charging the battery should be at 14volts from your alternator,any less than that and your alternator may be the problem.
I noticed on your other post you had some problems and they sounded 'earth' related.............bad earth terminal, dirty battery terminal,parasitic drain, they could all add to and/or create a problem.
At a push use a 12v bulb/holder and wire to test if you are getting a draw to earth (with key off) and remove fuses until you eliminate the culprit, if indeed there is any (you will of course get a draw because of the clock)
But in the meantime, clean your battery terminals and also clean and tight up all your earths

[KieranEbbett2500]

Hi, thanks for all yohe suggestions and tips. I will try that soon. I'll get a multimeter tomorrow and try and solve the issues. I have checked all battery terminals and the cables the one to the starter was a little loose but made no difference really. Also just to clarify the terminals are clean and tight. The build up of acidy stuff is along the battery clamp.

Thanks heaps.

[KieranEbbett2500]

Hi.

Although I'm still relying on the dash volt meter. But I'm fairly confident that it should be higher than 11.5 with the lights and fan going? During day time with nothing on it sits a needle width above 13 volts...

Is it just winter blues? (I'm from new Zealand) or is there something wrong?

Thanks again

[atom]

With lights and fan on (and even wipers) it should be at 12 volts or higher when above idle.
Nothing on should read 14 volts as already mentioned.