Flickering Battery Light. Alternator Problem?

[X5intheLandDownUnder]

I wanted to see if any of you have seen a similar problem. For the last several months my X5 ('02 4.4 L) with about 145,000 KMs has had a flickering battery light. It appears seemingly at random, but exclusively when in a low idle. It is a flicker and not a solid red battery light.

I've searched the forum and can't seem to find anything on the topic, but I asked my mechanic (not the BMW dealership) and he thought it was the alternator. I have had occasions where the battery has been flat after sitting around for a few days so I suspect he is right but I wanted to see if anyone else had a similar experience that was fixed with an alternator.

If it is an alternator issue - I see these are quite expensive (especially here in Australia)

Part II - Are re-manufactured Alternators an alright option to save $$?

Thanks!