I have left the Battery switch on and flattened the battery at least 3 times in four years, and notice from forum postings that I am not the only one. After the last occasion I put an amber light to the side of the main panel that indicates the battery is on, and it has made a difference for me - so far after a year, no goofs. If you have a panel that goes blank with the battery on and the avionics master off, something like this might be worth considering.
There's them that have, and them that will!
There's them that have, and them that will!