Shutdown cause: -104
It appears to be battery related. It may be related to -103, however both indicate that you should check the battery. Try running the laptop from the charger and see if the laptop still unexpectedly shuts down. Also check to see if there are any spurious sensor readings for the battery using iStat Menus or equivalent which may indicate the laptop trying to protect itself by shutting down.


  -103
  Battery cell under voltage detected.
  Check battery.
  
  -104
  unknown
  Check battery.


Source: Shutdown Causes