Jwalton314 at HTC Evo 4G Forum discovered that the HTC Touch Pro2's battery fits perferctly into the HTC Evo 4G.  They are the exact same battery after he looked up the battery specs.

Here are some tips to save your battery life:

With the HTC EVO 4G's large display and endless list of features, many have been worried about the battery life. While EVO users can expect about 6-8 hours of battery life with the default settings and average usage, that is not necessarily a guarantee - some users may experience longer battery life if they aren't using the phone frequently throughout the day, and heavy users may not get anywhere near 6 hours. We have done extensive testing with the EVO and have found that there are a number of things you can do to make sure you are getting the most life out of your battery as possible.

• 1. Screen Brightness
• 2. Turning off wireless services
• 3. Lower Screen Timeout Setting
• 4. Disable "Always-on Mobile Data"
• 5. Monitor "Running Services"
• 6. Turn off Background data & Auto-sync
• 7. Don't use a Live Wallpaper
• 8. Turn off features that use vibration
• 9. Manually Turn Off Your Screen
• 10. Turn Off Location Services

Cheers