fiio m5 battery drain to zero after fully charged and power off

My fiio M5 found battery drained to zero after fully charged and power off. The body of M5 is hot even power off. Firmware version has been upgraded to 1.4.7. After charged and power on, I found the year of M5 was reset 2014.
Since the firmware cannot downgrade, I can't test it is related the firmware version or the unit is faulty.

Does any C Hing encountered this after upgraded to 1.4.7?