Vaporfi REBEL II Manual Del Usuario página 9

CHECKING THE BATTERY VOLTAGE OR WATTAGE
To check battery voltage, press and hold the power down button until the level is
displayed.
volts appears as U on the display
4.2v = Full battery
3.8v = Half charge
3.2 = low battery, device will show LOU and battery must be charged.
NOTE: It is normal for your atomizer/cartomizer to activate at a very low voltage while in
battery check mode.
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