What should I do about my iPod Touch's battery?

I have had a 1st Gen, 16GB iPod Touch for a little under a year and the battery life is ridiculously short. Sometimes, it's even so bad that I will remove it from my Sony dock or USB wall charger and it will immediately turn off without me even using it. I have followed all recommendations for extending battery life I could find on the Internet: WiFi is always off, my brightness is at 30%, Push notifications and Location services are off, it has the latest firmware, and I charge it regularly. I am not sure what to do and I need a solution quickly becuase the warranty is almost expired. What is the next step I should take? Thanks for the advice!