Gday guys, hope you can help me.

The other night my wife left her interior light on and door open overnight, not surprisingly the engine wouldnt crank over in the morning.... I only got faint dash lights.

I jump started it and let it run for 5-10mins then switched it off but it wouldnt crank over again.... so I figure she's F**k the battery good and proper.
I jump started it again tonight and noticed the voltmeter sitting around 12.5 then slowly crept up to 13.8.... I put the lights on and it dropped back to 12.5 then I put the aircon on and it dropped below 11.

Now could a dud battery be doing that OR am I looking at replacing the alternator as well?
I have an alternator from an XH in the shed, could I use that? (its 100A)

The battery probably only needs a decent charge using a battery charger. Will need overnight or longer. I take it the courtesy light switch on the light switch was left on - with only a door open, the BEM will switch off interior lights after about an hour.

Thanks, I had it on the charger all night and most of morning with no difference. Also the light that was left on was the rear passenger side light at the grab handle.... one of the kids must have switched it on, was on faintly when I discovered the door left ajar.

Well I got the battery tested and it had dropped half its cells....only had 200cca.
I bought a new one and threw it in but its still not charging correctly so looks like a dodgy alternator.

Would it be ok to throw a 100A XH alternator into the EF which has a 110A alternator ??

Hey mate I got an EL fairmont and I no in mine I have a red light that comes on in the lower coner of the voltmeter should the alternator fail.I'm pritty sure the cluster in the EF fairmont have the same type of thing. but then again even if the light is not on thats not to say that your alternator is not still your problem. my 1st stop would b a new alternator. hope this helps

The Car needs to be running to be sure that battery light stay's on when running.

I remember when I drained mine while I did the headgasket that I assumed the Alternator might be dud because the battery light was on with just ignition, I assumed it was like the VN and it eventually went out...

The RACV man tried the jumper pack, didn't work, I had flattened the battery to about 0.10 charge I reckon, so he jump started off his own car and it went, I had to get a few leads on their correct position before it was running sweet, with lots of white smoke from the condensation build up and the ramaining water down the cat converter.

If the battery light stays on while the engine is running, then yes, get the alternater re-coed or get a brand new one or a wrecker one (don't trust all the wrecker ones).

Hope that helps

as far as i know they are infact interchangleable and shouldn't affect anything shouldn't being the word in this sentance.

as long as your not using stuff such as subs and amplifier's, etc, you should be ok