Sony HVL-MT24AM - Manual (Page 12)

1
Checking Batteries
The lamp on the control panel comes on or blinks when the batteries are low.
lamp on
Changing the batteries is
recommended. The flash can still be
used in this state if (Flash-ready
lamp) on the rear of the unit is lit.
Only lamp blinking
Flash cannot be used.
Insert new batteries.
 If nothing comes on when the flash ON/OFF button of the macro flash
controller is pressed, check the orientation of the batteries.