My dad charged the Jag battery up whilst he was here and drove it for a bit, he says the ameter showed the alternater was working. he turned the car off when he got back and then tried to start it half an hour later. He reckons the Battery is past it and needs replacing but I'm worried its more than that and it needs a new alternator, does it sound like he's right?

Whats the voltage accross the battery when the engine is running (also shown on the ammeter on the dash)?
If its reading between 14 and 14.7, the alternator should be fine. My battery gave up at 10 yrs old (90k)

[Edited on 5-4-10 by speedyxjs]

Yep. New battery. If its got 14v when running unless theres something big draining it down then id say the battery was buggered.

if he charged it and after only one start it was dead again then sounds like he's right.

Worth checking if there's an overcharging issue thats caused the battery to die though before replacing so try charging it back up and starting it. Stick a voltmeter across the terminals and make sure there isnt too much voltage from the alternator. It should go up to around 14.x with the engine running. If there's more then the regulator is kaput.

Assuming it's an older Jag with a battery that's a few years old, whip the plug/screw things out the top and see if it needs a top up.

Thanks for the replies, he said it was reading about 15 but I wasn't here so didn't see it. I'll make a note of your advise and wait till he visits again (I have to use jump leads to open the doors).

if its reading 15v then it could be overcharging or just trying to compensate for a shagged battery. Worth a check out with a meter.

I spoke to him on the phone and he's planning on taking it to the battery shop to get it tested, that way if it is dead he only has to make one trip.