2006 X-5 Red Battery Symbol light

Today I experienced a red battery symbol light after starting the X-5. THere was plenty of juice to turn over the engine. I drove the vehicle a short distance and shut it down. A few hours later I restarted the engine without incident-no red battery light. All appears normal now.
Could the main computer reset the light? Could this be an early warning sign of a failing alternator? If so, how many labor hours does it reasonably take to change an E-53 alternator? Thanks.