If you are referring to the GSX Pushback (in that case you should have posted it in the correct section), the problem doesn't have anything to do with GSX pushback but, most likely, because in the time it took to do the pushback, your battery was drained, and you haven't supplied an alternative power source in the meantime, like turning on the APU (if you airplane have one), or turning on at least one of the engines as soon the pushback started.
