Do you ever turn off your main battery or master BATT?
I do right before I end the flight.
That’s false. The main battery needs to remain on especially when flying. It lights up the instrument screen and it needs to be on for lights to work too.
U only turn it off after parking and after turning off engines
In summary, master BATT switch (main battery in commercial aircraft) is the very first thing to be turned on at the start when you load the game and the very last thing to be turned off at the end of a flight.
Yes, like many have said, the battery stays on for the entire duration of flight.
PLEASE DO NOT confuse this with APU, that is a separate thing!
You cannot fly without the BAIT/BATT, but can without the APU on (provided engines are running!)