iPod touch 4th generation battery life

I just upgraded my 3rd gen iPod touch to the 4 th gen because I wanted the camera feature. I am very disappointed with the battery life on my brand new iPod touch 4g. It would be completely drained by 3 p after a full nights charge with minimal use. I contacted apple tech support and after every trouble shooting method imaginable, they finally said I had a faulty unit so they swapped it out for me yesterday at the apple store. I came home, reinstalled everything again and let it fully charge for over 16 hours. Today, same problem. Battery was down to 50% after 4 hours of no use. I don't get how apple can claim music playback of 20+hours when the unit dies on standby mode after just 6hours. Any suggestions?