In Iron Man 3, Tony Stark has a problem powering the Mark 42 suit. There is a key scene where he has a panic attack because the young boy says the suit is not charging. There is also a scene where he is charging it from a car battery.
I've never understood this, as one of the major plot points of Iron Man 2 was Tony developing a new element for the arc reactor which could safety power his Iron Man suit and electromagnet in his chest without killing him.
Tony has the modified reactor in his chest since you can see the triangular shape through his shirt. So why is it suddenly a problem powering the suit?