On 1st generation Bolt Pro units, the column of LEDs on the face of the TX represents the charge level indicator for the internal battery.
Refer to item (A) on the diagram in the 1st Gen Bolt Standard / Bolt Pro : Quick Start Guide.
The top three blue LEDs indicate the relative charge level (> 75%, 50%, 25%)
The bottom LED comes on when the internal battery is running low and has two states:
- solid red: battery is getting low
- blinking red: battery is about to die
Items (G) and (E) on the TX indicate whether the unit is accepting external DC input, and whether the internal battery is charging, respectively.
If the bottom LED remains red, or continues to flash red when known good external power is being supplied to the Bolt Pro TX, this could indicate a hardware issue with the unit and it would require examination by Teradek's technicians.