i had this happen the other day with my microjet, the batter moved just enough to crush the elevon a little, not bad tho.
but a bigger danger is if you've got a car with the rear seats down, if you crash you then have that 12V battery just waiting to fly forwards and hit you, followed closely by the flight box and tranny. maybe its just habbit, by my heavy items are on the other side of the car from me, unlucky passenger, spose i should put those items down behind the front seats....