Power off- on

I have a Ford Edge del 2009 I going to dealer to replace a
whole transmission and replace the battery but since the
make a change now the car anytime is off and sometimes
on again alone just I wanted know if you know the
problem because is dangerous sometimes I going in
freeway and motor off like is die and few seconds after is
on alone and when not I on again in the freeway or street
than happen 2-3 times a day and I can't go in the streets
with this problem