Hello I will help you with your question,
It very likely is the alternator but some testing is in order before replacing it. If you have a voltmeter you can test for battery voltage with the engine off/key on at the connections on the back of the alternator. Let me know where you find battery voltage.
If you do not have a voltmeter you can stop by an autoparts store and they will inspect your charging system with their equipment, the battery will continue to run the engine for a short time but will fail eventually
Let me know what I can do to help you with this