I have a 2008 Civic EX. A couple weeks ago my car wouldn't start when I left the post office. I turned the ignition several times got nothing then finally it barely weakly started up. It drives fine once started. I live in Las Vegas my battery was just about 3 years old so I figured I need a new battery. I took it to Autozone my battery was still under warranty so I got it replaced for free. I immediately noticed it started up strong with new battery. The past week I noticed it sounded weaker when I turned the ignition to start the car but forgot about it. Tonight my car wouldn't start in the parking lot of a grocery store. I eventually barely got it to start after several attempts. When I got home I turned it off and immediately turned it back on it started right up but I have a feeling it might not start tomorrow morning. It's a brand new battery. I thought if it was the alternator it would die while the car was running? That does not happen. Everything is fine once I get it started.

 

Your alternator is dying. Happened to my civic