The Tevion machine is now re-badged as an Audiovox D1708PK.
You would have more luck now, searching for the Audiovox branding on the portable player.
This online retailer still has it for sale and I add the phone number below so you can contact them about getting another battery pack.
Toll Free: 877-285-8723
9:00AM - 5:00PM EST
Monday - Friday
Also PC Rush, a store under Buy.com has this product and contacting them may help you obtain a battery.
Customer Service Toll Free (US Only)
This link here
, is for an external battery pack and is on Ebay.
If I can be of further help, let me know,