1994 Ford Escort Battery is not charging

My 94 ford escort died while in motion last week. I had the battery tested and found that the battery had bad cells. After replacing it a few days later the car died again and would not start or even jump. So I took the new battery in and founf that it was bad as well. After replacing yet a nother battery I had the car tested at the local auto parts store. The alternator was only putting out 6 amps. So I replaced the alternator. A day later after driving at least 50 miles the car did again the same thing. It died and will not jump start. I am assuming I have yet another bad battery that wasn't getting charged properly. Some one suggested since I had already replaced the alternator that I should look at the Voltage converter? Any ideas?