From the owners manual:
When the light is switched off, the charging state indicator [1-1] displays the operating state of the integral battery for the duration of the charging process:
Charging state indicator green - flashing
Integral battery is charged at maximum capacity.
Charging state indicator green - permanently lit
Integral battery is charged to 80% and then charged fully with a reduced current.
Charging state indicator red - flashing
General fault indication, e.g. incomplete contact, short circuit, battery faulty.
Charging state indicator red - permanently lit
Battery temperature is outside the permitted range.