Clear the message from the screen (hit OK button).
Turn off the car, turn it back on, see if it goes away.
If it goes away, watch for its return.
If it comes back, call the dealer.
Also, check to see if the little wrench is showing on the driver's screen.
There are two reasons to keep car plug in or on when not in use. One it can keep battery at a nice temp. This forum does not talk about keeping the cells balanced. But they need to be from time to time.