I have a purple Cube and under power of only USB it is 4.9v which is typical in this type of hardware. When under battery power my voltage jumps to 5.25v…
Is this normal?
It looks normal. It depends of your power supply that power the Cube. The power brick mini (provided with standard pixhawk Set) provide 5.3V to power the Cube.
5.3-5.4v is the normal voltage