Its ok, i also get this message since my aftermarket unit, has a sleep mode to wake up in about 1 sec when i turn on the car.
My car audio digital capacitors and my multimeter shows a solid 12.5V after engine shut down and 14.5-14.8 solid when the car is running depending on the RPM.
It is just a stupid warning with no real benefits to it.
My guess is that who ever got this message, have something that is using car battery power after shut off and the system detects it- for sure.
Never ever i had this message when i didn't had an aftermarket headunit, just when i was playing music and the car is off.
Could be a dash camera in the wrong fuse, OBD device left in the port (it works for hours) Etc.
One cool feature though is that one where once in a 2-3 years it will tell you to replace key fob battery, well that's cool.