HELP? New battery needed or just bad earth?

[Paul67]

I have an intermittent problem starting my car. It's only happened twice in the last few weeks, both times after starting the car from cold and driving to the local corner shop and then trying to re-start the car minutes later. I turn the key and the dash lights up but wont start or turn the car over even.

Both times I have checked and cleaned the earth connection on the battery and then it starts up fine.

Since then I've read a bit about car batteries and cold cranking amps, so today, while visiting my parents, I was going to test the battery with my father's multimeter to see if the voltage dropped very low while starting the car. I first tested the voltage with everything off and it showed about 13 volts.

I had to wait a while for a second pair off hands to come and start the car while I tested the battery so while I was waiting I decided to test the battery with the radio on and the heater fan on but the engine off, as I sometime start the car with these on. This time the voltage was about 11.

Then when the second pair of hands (my nephew) eventually turned up I was ready to test the battery as it was being cranked but the bloody thing was too week to even turn the engine over let alone start the car! It seems me putting the radio and fan on earlier had sucked out that little bit of power I needed to start the car.

Anyway, I had a suspicion the car may start if I left if for 10 minutes, and it did, but was then to afraid the turn it back off the test it on a multimeter while restarting in case it didn't restart afterwards and I had to leave my car parked in my parents drive overnight!

I could possibly retest it again tomorrow (this time while parked on a hill ready to jump start it..) but was wondering if this sounds typical off a bad battery or perhaps even just a bad earth? The latter, of course being, a lot cheaper to fix... and I don't want spend money on a new battery if I don't need one quite yet, not least because the weather will be a lot milder next month and wont need as many cranking amps to start the car.

Any advice is much appreciated, thanks!

[Dave]

Hi mate. 13volts when everything is off sounds about right, and you're correct that the cranking does take a lot of power when starting up. it sounds as though the battery is fine (though its always hard to say for sure!). As the car fired up after you had disconnected the earth/reconnected it, I would have a good check to make sure the whole earth cable is intact. Give both the terminals on the battery a good clean up with a wire brush, and also the connections on the ends of the live/earth cables. Make sure they are both connected up good and tight, and cover them with a light layer petrolium jelly or something similar.

It does sound like a bad connection, so best (and cheapest!) to start there first.

If you can, get the test meter and test the car when starting to see what readings you get (after you've done the above ). Also, see what readings you get on tick over, and with a slight rev (to around 2500rpm).

It's good practice to make sure everything (electrical) is turned off when starting the car, as it saves putting extra strain on the battery. I always turn off heaters/radio/lights etc before I turn off the engine, that way everythings already off when it comes time to start the car.

Are there any other symptoms?

Hope this helps!

[simpo]

Wat about main relay?

[Paul67]

Cheers Dave! Will do those things a little later when I get the chance. And no, there are no other symptoms.

Simpo, do you mean the main relay in the fuse box under the bonnet, and if so wouldn't I hear it clicking if it was faulty?

[ryan..]

The problem with these things is it could be a whole number of things.

It wont cost much to completely replace the earth lead. That way you know 100% its not corroded inside the cable

As a general rule:

12.6v is float voltage for a 12v car battery

14.4v is with the engine running (this can change depending on what the alt is upto though)

You will see drops to about 11v when you initialy turn the car over as it does draw quite a bit of current. The best thing to do regarding battery voltage is do a few checks over a period of time.

Check it with the engine running and all electrics off (stereo, heater, lights etc etc)

Turn the engine off and keep checking it and watch the voltage drop till it settles.

Check the voltage after its been sat for about 3hrs or more

If its dropping really fast when you switch the engine off then its a sign it might be on its way out.

If it drops below 12v then you need to give it a really good charge to try bring it back to life

[Paul67]

Well, the same thing happened today. It wouldn't turn over, so I left it a few minuets and then it started fine...

Following your advice, Dave, I started cleaning the connections and after checking the earth, which looked good, I immediately noticed the live connection on the battery, although secured very tight, looked like it needed a very good clean. So I cleaned it and, after reconnecting the battery back up, I noticed my interior light seemed brighter.

So somewhat convinced this bad live connection would have been causing the problem, and before I went through all the other connections.., I decided to park up on a steep hill, turn on my headlights, put heater fan on full, radio on, rear demister, hazards and every thing else on inside the car too, for a several minuets before attempting to start the car, and yet, despite the extra strain I put on the battery, it started up without any problem! It definitely would not have done that before I cleaned the live connection!

So, it certainly looks like my intermittent starting problems are now fixed. Having said that, when I get the time I will check all the connections/grounding point etc, and also do what you recommend as well, Ryan.

Thanks for all the advice, it's saved me spending about £60 on a battery I didn't need! Happy Days!!!

1"£££$££"!!