Check out eieio's post in the battery section. Not guaranteed to work but some people notice a difference. In a nutshell:
1. Charge phone while on til light is green.
2. WITHOUT unplugging hold power button and choose to shutdown phone. Let charge til green.
3. Power phone back on and etc. etc.
Repeat those steps until there is a 1-2min delay in LED turning from orange/amber to green.
But like I said, eieio posted that in his battery thread if you need it a little more in depth.
P.S. Just looked it up, it's the first sticky on the EVO 4G forums, 'Possible Battery Fix from HTC.
Enjoy!