2009 nissan altima starting problem?

Twice my altima has not started, once a couple of years ago and again yesterday. Brought battery in, charged it and starts OK. What I did notice this time is that the brake pedal would not depress while the battery is flat,so that the push button starter will not activate. Is this a reason for non-starting or is it the result of a flat battery? Now that the battery is recharged the pedal depresses as normal. One would think that in some way the battery and brakes are electrically connected.