Is it the belt or the alternator itself?

[Delia Caribbean]

4.4i 2000 - The red battery light is on, the car's engine is not running as smooth as it used to. I've not used it for four days but it starts OK. Without looking at it - I'm waiting for the mechanic to come - and I don't know him and don't trust mechanics much - how can I tell if it's the belt or the alternator that's probably at fault?

[primetime]

Need a few more details on the symptoms...But its probably the battery. When was the last time you changed the battery?

[Delia Caribbean]

Not changed it in few years. I got battery checked two months ago by BMW dealer - they told me the battery had not been changed in 5 years and told me to buy a new one at EC$1000 = approx US$370 and charged me $75 to tell me that so I went elsewhere. The other garage said they'd tested the battery and it had lots of life left. Last two weeks though, when I turn the key, a few times it didn't turn over on the first attempt, but did on second attempt. What do you think? By the way, excellent voting choice!!

[Delia Caribbean]

UPDATE: I just left the engine running for 10 minutes and it cut out. Won't start. Clicks when I try to start it - just like it did before - got a jump start then and it was OK. Not sure what to think now...

[primetime]

Its the battery...Thats exactly what mine did before it finally died. It gave me the battery warnning and started slow for a few times and then finally just died...I changed the battery and no problems since then...

Just saw your update...See what happens after the car is on after the jump..if it cuts out again...like in the middle of your drive then it probably is the alternator...That happened on a 5 series I used to drive..the damn thing would cut out in the middle of my drive...jump it again..and a few minutes later same thing would happen. It was the alternator...

[Delia Caribbean]

but my engine is idling badly - never did that before!

[Delia Caribbean]

Thanks, but that doesn't explain the bad idling... it happened just before it stopped the first time and it's still there.

[Big "J"]

Alternator probably drained the battery. When the battery goes, electronics go haywire and the engine depends on good electronics, hence rough idle. start with your battery and then have your Alternator checked.

[Delia Caribbean]

I've arranged to get battery charged tomorrow. If I do so and the red battery light goes, does that mean I need to change the battery and it's not the alternator? I agree with you, I'll get the battery tested regardles. However, the manual says, "Red: stop the car as soon as possible. the battery is not being charged. The alternator V-belt is defective or there is a fault in the alternator charging cicuit. Consult the nearest BMW Service."

[Big "J"]

We have some pretty heavy duty batteries and can keep our cars alive for a lot longer than most others. Once the Alt. goes then the battery takes over and some of your electronics will start acting weird. The alternator should be check before you replace the battery if you're getting the red indicator.