If the battery light indicator went on in your cluster, your charging system was not working properly. In other words, your alternator was probably on its way out.

It doesn't surprise me...I have an 04 X5 3.0i and my battery light came on @ 61k miles. Turned out the voltage regulator on the alternator wasn't accepting a charge. I just picked up an OEM Valeo Alternator for a real good price and swapped it.

I think you did the right thing. When my battery light went on, I took it to the dealer just to get a rough estimate on how much it would cost to repair. The SA gave me a general estimate of $1380 to replace the alternator, 2 belts, and 2 pullies ............ So I turned around and ordered the parts online and did the work myself for a little over $300.