These cars don't seem to like being left idle and unlocked. Even if the infotainment system is switched off.
I've noticed it a few times, where say I've been washing the car (car unlocked with key left inside it). Next time I drive it, post-wash, the infotainment system takes a while to get going, that whole "loading settings" malarkey. And I've had the low voltage error ping on the dash too, typically if sitting in the car with the radio on, even only for a few minutes.
It always resolves itself once you've driven it a bit and its "charged up" again I guess.