Battery replacement intermintent on, then permanently off

I just replaced the battery in my iphone 3g yesterday. I put everything back together and powered the phone on successfully and charged it all the way. I made phone calls played games the works, no problems. Then today I went for a motorcycle ride with my phone in the jacket. It was cold out but not wet. The phone would turn itself off at random. Now tonight I was listening to some music on the ride home and the phone shut off for good this time. I tried taking it apart and placing th old battery back in but its a no go. Nothing happens. I tried powering it on with just the sleep/wake button and holding that plus the home button for over a minute. Nothing. Please help guys.