Its done this once before 2 weeks ago and I took it to a mechanic who said it just needed a new battery; got the battery and just yesterday it did the same thing; breaking down in the middle of the road. got a jump and it ran fine and starts every time but im afraid to take it out now. I checked the alternator by removing the black wire from the battery while it was running and that seems fine, so what could it be and how do I fix it? Thank you.