g dosch, based on the 120GB storage space alone, this would be a 3rd gen. The following generation is the HD and it does not have that capacity, nor did any of the preceding generations. Besides the larger capacity, there was also a firmware update for the Zune, Anyhow, the battery is readily available at places [http://www.megacapacity.com/8883.html|like this.] If you need any instructions, check [http://www.rapidrepair.com/Merchant2/merchant.mvc?Screen=zune120|on here.] Hope this helps, good luck