Here is an Aiwa AM-F70 Portable MiniDisc Player/Recorder.

Includes:

Player

5 Blank Discs - 74 Minutes

Third Party 3D Printed Gum Stick Battery*

USB Charging Cable

This player used a proprietary rechargeable battery.

I found this third party battery on eBay and it worked! I get about 4 hours of continuous playback.