It is likely that newer vehicles will drain batteries over the course of say 6 months. Idk if it's the norm, but I've heard it before and experienced it with a fleet of brand new trucks that were parked for 6 months. A 30 year old truck and most of the 5-10 year old trucks starred as did most of the equipment with master switches. But the brand new trucks were all dead. They also recharged after being jump started so good chance the batteries in yours aren't destroyed.
The safe way and proper way is to recharge them completely though unles you plan on hopping in and driving it for hours straight.