Driving on low battery; bad for the alternator?

[autoque]

The X5's battery warning light has lit up and the welcome light doesn't turn on anymore. The car still starts fine, but if I drive in this low voltage condition, is this going to be bad for the alternator? I need to wait until next week to get it serviced. The 2008 has only 2500 miles on the odometer. It had once completely discharged before, to the point of being unable to start at all, by leaving it untouched for six months. The battery failed again, so I jumpstarted it but now it's showing a warning message and the steering wheel won't move to a position when I start the car. I'm afraid it might be hard on the alternator.