Flat battery

Tony Houghton ( snipped-for-privacy@realh.co.uk) gurgled happily, sounding much like they were saying :

Have you checked to see if it IS charging?

Put the voltmeter across the battery terminals - you should be seeing somewhere around 13 volts at idle and 14-15 at anything above about

It's possible the one you bought could have been sitting on a shelf for long periods sulphating away without being maintained.

: That time : we weren't in a hurry so we took the battery out and put it on charge : for an hour, which was enough to start it again. It went OK today.

Car batteries can appear to be flat when they are not, as a result of a continuous small drain. Something builds up on the plates (I am not a chemist, thank god, so "something" it is) which stops it working properly. A short charge, which reverses the current, is enough to knock of the crap and resume full vitality. That's why leaving lights on for just an hour or two can appear to flatten the battery, which is fine after a very short charge.

So ... I'd be looking for a small but significant current drain when the car is nominally off. It might be as trivial as a boot light coming on: I had a Beetle which could do this to a battery if the radio was left on overnight!

Ian

redwood ( snipped-for-privacy@nooos.com) gurgled happily, sounding much like they were saying :

No, I didn't.

Ian Johnston wrote: >

Can that happen to any car battery or does it only tend to affect ones that are in bad condition?

I don't think the 0.02A we measured would be significant? Funnily enough I did check the boot light (luckily the rear seats fold forwards) because my dad remembered a case years ago with a colleague's car that wouldn't start on Monday mornings.

: Ian Johnston wrote: : >

: > Car batteries can appear to be flat when they are not, as a result of : > a continuous small drain. Something builds up on the plates (I am not : > a chemist, thank god, so "something" it is) which stops it working : > properly. A short charge, which reverses the current, is enough to : > knock of the crap and resume full vitality. That's why leaving lights : > on for just an hour or two can appear to flatten the battery, which is : > fine after a very short charge. : : Can that happen to any car battery or does it only tend to affect ones : that are in bad condition?

Any one, as far as I know and in my experience.

: > So ... I'd be looking for a small but significant current drain when : > the car is nominally off. It might be as trivial as a boot light : > coming on: I had a Beetle which could do this to a battery if the : > radio was left on overnight! : : I don't think the 0.02A we measured would be significant? Funnily enough : I did check the boot light (luckily the rear seats fold forwards) : because my dad remembered a case years ago with a colleague's car that : wouldn't start on Monday mornings.

That's probably not enough - but you have an intermittent problem, as I understand it, which probably means an intermittent fault.

Ian

I really wouldn't rule the battery out yet. Test that the battery is being charged when the engine's running - if it seems to be then I (personally) would replace the battery without hesitation, seeing as the quiescent current is negligible.

Hmmm, just noticed the car's a diesel - need a healthy battery to crank the high compression on the engine. Out of interest, car model, engine size and battery manufacturer and capacity?

Mike Dodd wrote: >

Yes; that would probably be the first thing to try replacing if we can't find any other fault.

It's a Rover 420Di (2.0 turbo direct injection). The battery is a Pavilion 75AH. I suspect low price was the main thing in its favour.

Ok sounds like the battery IS being charged or driving it would not have restored it.

Check/adjust or disconnect the boot/tailgate switch & light. Perhaps light stays on when the boot is shut sometimes. You mentioned shopping.

Perhaps you can pull the fuse on all the interior lights to see if that fixes the problem.