Stalling

I need advice becuase I have no clue what else to do. I bought my girlfriend a car (1994 318CI) 2 months ago and since then the car has stalled out several times while she was driving. Many times it stalls out and does not start back up. One time the entire car died, lights radio, and everything else just shut off. I have sent it to a mechanic twice and it doesnt take long for the car to come back into its old habits. I need help with this because I am about to beat the car with a shovel if I have to pick my girlfriend up again because of this car.

How good are your mechanical skills?

Battery, alternator,bad grounds,bad or corroded connections on the starter. security system malfunction. How about some more info?