I have a 1966 Mustang with 150,000 miles. Everything was working fine and then one day it would not start. I was able to jump start it from a friend's car and figured the battery was dead. I drove it for 30 miles on the highway to charge the battery but after I turned it off the battery again appeared dead. I changed the battery and had the same problem. The battery has 12VDC at the terminals but doesn't appear to be putting out enough current. The alternator is supplying power to the battery, I checked the voltage while it was running, 14VDC. Off of the car's battery it will not even turn over but starts fine off of another car. Please give me any suggestions you might have. Thanks, Ethan