iPod touch 6th gen battery replacement for 500 hours of music

I have a 6th generation iPod touch with over 500 hours of music that I have downloaded to my Itunes library on the device I went to my local Apple Store and was informed by an Apple associate that the battery cannot be replaced. this is contrary to what I have read on line. I would very much like to have the battery replaced so as to access my music while traveling.

Is it possible to replace the battery and if so what is the cost ?

[Re-Titled by Moderator]