need electrical help

[thundercat2]

batteries been weak for about a month and car wouldn't start on thursday morning.i had been having a problem with flickering headlights prior to that.bought a "red top" and put it in but 10 minutes later at a stoplight the car died on me.now the strange part of this is in order for the car to start again i had to be pushing on the brakes.no cluster lights or anything but step on brake pedal,all needles jump and odometer lights up and then it starts.also once in a while starter will grind a little while starting.
could i just have a bad starter or am i grounding out somewhere?

ron