I used to have two of these units and recently sold one. This one plays and records minidiscs fine. The battery is about 4 years old (after market - purchased on eBay). 
The docking station will charge the battery, but this battery may not hold a charge for very long.
The unit will play fine when in the docking station and connected to AC power (included).

What's included:
  • One (1) Sharp Mt877 Portable MiniDisc Player/Recorder
  • One (1) AC adapter
  • One (1) plastic charging station/dock
  • One (1) "gumstick" rechargable battery pack
  • One (1) TDK blank MiniDisc (80 minutes)
  • One (1) Removable Keychain cord
  • One (1) AA external battery pack (not shown in pics)
What works:
  • When docked in the charging station and connected to power, the unit will play and record MiniDiscs.
  • The unit will run on a charged battery pack.
  • When a stereo microphone is connected, it records in full stereo.
  • The display screen works.
  • The kickstand on the docking station works.
  • The green and orange LED lights work to indicate various functions, including charging.
Be aware:
  • The middle status light (blue) doesn't illuminate for some reason. Does not affect anything.
  • When using the device for a while, sometimes the display screen "fades" out, but then comes back to normal. I'm not really sure what the cause of that is. But the device doesn't stop playing or recording.