Ok, so you would think mechanics would have a little more common sense than this. The first thing that came to my mind was either the gas, or electricity, cuz that's the only thing that would cause it, but I would think they can figure that out. So I didn't bother to tell them, and so I didn't mention anything. Well, I come to find out that the other engine they put in was also doing the same thing. So, at the end, the guy told me it was the alternator!!!! Can you believe that?!?!? That's one of the first thing that came to my mind, but thought they can figure it out if it was that. Well, they put another battery on the car, and since then, the car is running fine. Thanks a lot for your help, and next time something happens like this to you, make sure you tell them if they check every posibility before they swap the engine.