This is a total misdiagnosis. It's always possible to get a new car with a bad battery but not four of them. No way on earth; unless you're the unluckiest person ever born.
This sounds like an abnormal parasitic draw to me no matter what they say.
If you want to do a quick test (and assuming no VOM, test light, etc) make sure the battery is fully charged with the battery negative cable disconnected. Lightly touch a sharp edge of the neg. cable end to the battery negative post in a subdued light (dusk, in a garage, etc.).
If you see a bright blue spark, even a small one, then you have a parasitic draw worth worrying about. If you see a faint yellow spark then this could be ignored since that is probably the clock at work.
That's not a real scientific testing method but can work in a pinch.
(And a good battery is not going to go flat in 5 day on its own.)