I successfully installed a new battery in my iPod video U2 edition (5th gen). Powered it on and the iPod reported that the battery was fully charged. But then the dang thing wouldn't turn off.
I tried resetting the device - hold [Menu] and [Center] for 10 seconds until reboot. Apple logo displayed... That didn't work either. After reset, still reported fully charged and wouldn't power off.
But here's what worked. I connected the iPod to my PC, opened up iTunes, and chose [Restore] from the iPod menu. That restored the factory settings and wiped out all the music on the device. But now the iPod powers off and reports the correct battery level. I resync'd my playlists and my iPod is as good as new.