Why battery light turn on frequently on 2006 Ford Explorer

I have a ford explorer 2006 and the battery light turn on frequently, already check the voltage of the battery and the alternator has the required voltages.

2 answers
When the vehicle is running, take the pos. terminal off. If the engine stalls, the alternator is bad,take it to an auto parts store and have them test it to make sure
sounds like your alternator is on its way out