Normally when I switch off the master, my 3500 switches over to battery mode along with the red bar at the bottom showing the countdown to shutting off.
At the end of the last couple of flights, I've had to manually shut off the unit after switching the master off as the red bar countdown no longer shows up.
Instead I only get the "check volts" warning and the efis remains on unless I hold the middle button in to shut it off manually.

Any ideas ?

I've also noticed during the last flight that the X-wind/wind direction readings were displaying an incorrect direction and kt readings. ???