2001 Ford Escort Battery Light

I started my car and let it run for about 20 minutes this morning before taing off for work. It was about 5 degrees here in Ohio. While I was driving my battery light came on, flickered at first then stayed solid. After about 20 miles my radio quit working, and my panel dimmed, turn signals didnt work and I can only assume my lights were not working. By the time I got to work the car was making a chugging motion, but made it. When I turned the car off the radio came back on as did everything else. Can you tell me what this may be? I just had a tune up and batery changed out in June. Thanks for your help.
Katinamarie Mendoza