new battery won't hold a charge, what could be draining the power off?

What is your question?

We keep replacing the battery but none of them have held a charge. The auto shop says there's nothing wrong but we have to charge the battery if we want to use it. Sometimes we can be somewhere and the van has ran good up to that point but if we turn it off, it won't start again. I am not sure if it is 5.7L V8, or 5.0L V8.