Why would the 2000 Ford Escape drain its battery after 2 hours of use? on 2001 Ford Escape

The battery light would come on. When starting on the starter knocks.It would not start? Until I recharge the battery again it would start.

2 answers
car won't start with insufficient charge in battery. battery draining cause charge system has failed. most likely the alternator. have battery and alternator tested.
poss charging system is bad