Only one Battlechest per Battlenet account?

Hey,

I've recently watched a guide about RAF yourself and wanted to order a Battlechest key to give it a try. The shop notified me that only one Battlechest per account is valid and I should check it first. So there's no way to add another Battlechest again?

I've seen streamers who have about eight WoW accounts inside their Battlenet account. So what's true now?

Thanks in advance.

Best Regards