For whom interested, the legend for battery state indicator (3 LEDs) is as follows.
Green: Vbat ≥ 7.48V;
Amber: 7.48V > Vbat ≥ 7.0V;
Red (steady): 7.0V > Vbat ≥ 6.47V;
Red (blinking): 6.47V > Vbat ≥ 5.45V;
When Vbat < 6.47V the box keeps both DC outputs disconnected from the battery to prevent battery over-discharge.
Battery state indicator works only when the USB port is turned on.
The box works fine with two cells loaded (supports 2s battery configuration).
Ingress protection is IPX4, not IP67.
*All the voltages are measured at room temp (25 degree C).