Did you try to reset the iPod by holding the sleep and home button for about 10sec, until the Apple logo comes back again? You will not lose data doing a reset.
If this does not help, set it up as new device, first without using the backup, in case it contains corrupt data.
If the battery life is getting better, try again, this time using the backup, to get all the settings and data back.
Should it get worse again after that, you had corrupt data on your device, causing this problem. Restore again without the backup.
More battery tip here: