HULKMAN Alpha's DC port is marked as 12V, as the same as the standard voltage of the most on-board electrical appliances. In fact, the designed standard output voltage of the jump starter is 15V, not the marked 12V.
The more jump starter battery power remaining, the higher output voltage.
Although the designed output voltage is rated at a value, actually, it will fluctuate with a range.
Note: Don't worry much about the difference, our safety features provide you a peace of mind.
However, 15V output voltage may cause your own devices to fail to be charged:
1) You'll see a charging error on your own charging devices when using the 12V DC output port with your HULKMAN Alpha jump starter in a fully charged.
2) When the HULKMAN Alpha jump starter is fully charged, the output voltage of the unit would be higher than 15V, sometimes even higher than 16V. When your device detects that the input voltage is higher than 15V, it will start its own charging devices' over-voltage protection automatically. That may cause your own devices to fail to be charged:
3) Avoid charging your device in a fully charged when using the 12V DC output port.