gizDuino(arduino clone) doesn't power up with 7.4v battery
The power supply input goes to a 7805k regulator which feeds the MCU. The 78xx regulators need about 2 to 2.5v higher input than the rated output to work properly .
My guess is that the regulator was able to work correctly while the battery was full and stopped working as soon as the battery voltage dropped to 7v or so.

Also note that the datasheet of you device specifies an input voltage range of 8-12v for the power supply input, so the input you are trying to use is out of spec.