The batteries were already included and inserted in the device when I bought it.

I mean that the batteries were not inserted, but were included in the package. But was the packaging no longer sealed? There should have been an adhesive seal on the openings. But I can't remember exactly what happened to the batteries, but even if they were, it's quite possible that it was changed at some point.
To be 100% sure, why don't you contact Braun customer service?

Unfortunately I can't remember, it's been too long :-) Is there anything on the packaging?