started ok then battery light came on after idling for 20 mins?

In order of likelihood:

Slipping/knackered auxiliary drive belt. Alternator low output. (One diode failed, or brushes low?) Loose/dirty connection in the charging circuit.

If you have a reasonably accurate meter, you can measure the following voltages across the battery:

When it has been standing all night. When first started with no extra load. At idle with everything switched on. At fast idle with everything switched on.

You can either post the results here, or look online for what they should be.

Should it not be possible to carry out those tests, seek help. If an AA/ RAC member, they carry automated test equipment that is reliable. If you have 'Home Start' you could always suggest that it wouldn't start ;-)

Chris

thanks chris will try that....

Got feeling battery is fairly new. looking for receipt... :-)

[...]

It's pretty unlikely to be the battery.

Chris

You'll spend more warming it up by idling than the cost of a new alternator.

Some US cars can be started remotely - think TV remote. So you start it

20 mins before you want to set off, and it's toasty warm when you want to go. And to hell with the planet!

Or cool when you need it! We had a hire car with the remote start option. It was very handy for reducing the cabin temperature to tolerable before entering it.

Tim

Problem found. Alternator belt snapped.

A friend of mine had the same fault: Cold weather, started up, left it running, came back to no charge and the belt snapped: Cause: frozen water pump meaning the belt slipped on the pulley till the belt heated up and dropped apart. Cure: add anti-freeze and renew belt. Also seen when the aircon pump seizes.

Unless they rushed it and only 1/2 filled a cell. No doubt it appeared full when they capped it, was 1/2 full when I got it home. They don't last 6 months after starting a few times like that.

Didnt think of that. Water didnt look frozen though.

In article , paulfoel scribeth thus

Sometimes .. the simplest things;)...

No air con so its not that. Didnt snap whilst idling only when car got around corner.

Did get me thinking though. But checked anti-freeze using sprygo and its ok to about -20 by the looks so i dont think its that.

funnily enough though it looks like it was fitted on back to front! i.e. rubbery bits on the outside. Guess this is not cool.....

I'd hope it went through some sort of window/sunroof opening routine before trying to cool the interior down from 60C . . .

Rob

We're talking about the country of free gas here. Don't be daft. ;-). Besides, would you really want your car windows opening when you're not close enough to apprehend a tea leaf?

Tim