Now that I have my truck (47 3600 with a 235) back on the road Iv been driving it every day. I was driving it about eight miles to the next town where I was doing my student teaching. I never had a problem. Now that I am subbing in town I don’t get out on the highway, my battery isn't charging. I have an alternator on it so I thought that would take care of the battery even on short runs. Any ideas?