Car alternator?

My car shows battery warning when driving at night. One time I drove to buy stuffs at the town, battery warning glowed and the steering went a little heavy. And so I went on, parked my car, and went to buy things. When I went back to the car, it wont start and started to produce ticking sounds. I called my mechanic but he was out of town but instructed me to get my car pulled to his shop and so I did. I went there the next day and he said either the battery is dead due to old age, or there's something wrong with the alternator. He's not an electrician. He's a mechanic. Hope you can help me. Thanks guys, and more power!