OK The same thing just happened to me .
I'm at work on a friday alone on phone duty listing to streaming music on my evo that is pluged into my computers usb. Suddenly the music stops. I thought it was a data issue with the stream. I was going to change the channel an saw my phone was off. My charge light was not lit but I was still plugged into the computers USB. several attemps to turn it on with little more than a failed attempt to start up led me to this forum. Having read about the battery being suspect I pulled it out and it was warm. I sprayed it with instant chill and tried again still with failed attemps. I pulled the battery and tested it with a voltage tester. There are 4 contacts on the battery. the outside one closest to the edge is a positive and the other 3 are negative. I tested 2.6 volts offthe positive to each of the 3 negatives. I pulled the test leads out of the tester and used alligator clips to connect them to a 12 vold alarm battery . Holding the positive lead to the positive connection on the battery , I quickly tapped each of the negative contacts a few times with the negative lead from the 12 volt battery. ONLY FOR A FRACTION OF A SECOND TAP EACH TIME. After repeating this a few times I rechecked the battery voltage again and fount the battery had come back up to 2.9 volts!!! I repeated this procedure again and rechecked my battery at 3.1 volts. Not wanting to press my luck further , I placed the battery back into the phone and it started to charge right away. I turned it on after about 3 minutes without issue. 10 minutes later I am at 18% no that's 19% and climbing. Hope this helps others with this issue. Glad I found this forum, otherwise I would not have had any idea where to start. Warning!!! DO NOT HOLD LEADS TO THE BATTERY! , ONLY A QUICK TAP TO THE CONTACTS TO BUMP IT. OTHERWISE YOU MIGHT CAUSE THE BATTERY TO GASS OUT AND POP!! DO NOT ATTEMPT THIS IF YOU ARE UNSURE ABOUT WHAT YOU ARE DOING AS I WILL NOT BE RESPONSIBLE FOR YOUR BATTERY OR PHONE ! Those with an understanding of how batteries and chargers work , or anyone who has properly jumpstarted a car will understand exactly what I just did.
Oh BTW 28% and climbing!