Constantly having to jump start?

Had an incident a few months ago where I was driving and all of a sudden, the car lost power, I mean you could push the pedal to the floor, and it wouldn't respond and then it shut off. Ended up getting it to the shop and mechanic couldn't replicate the issue, car ran fine for him. Got in to go home got two blocks and it did it again. The mechanic came and towed car ack to the shop. I don't remember why but somehow it was the alternator so that was replaced. Drove fine for about a month and happened again. The mechanic said a bad alternator, something about pigtail wire had burnt. Anyway, he replaced the alternator at no charge. Long story short he has replaced that alternator three different times and this last time he got an alternator from Nissan. My problem is with a new alternator and battery is why am I having to use my portable jumper every time I start my car?