Chevrolet Repair: Battery will not hold a charge, jumper cables, bread truck

Question
Hello!
 I recently purchased a 1979 chevy step van (bread truck) I have changed the battery, alternator but after two days or so the engine will not turn over. The battery is always charged fully. What can I do? Thanks, Henry

Answer
Henry, Help me out here. You say the battery is "always fully charged" and the engine won't turn over. How do you get it to turn over? Jumper cables? Does the starter make any noise at all?

looking forward for you answers to my questions so I may help you

Mark