You need to understand what you are doing with them , they currently are various resistances ( I have 5.2ohm and 5.0 ohm ones ) these will work OK at 6-7 volts , It takes some math ( Ohms law calc. here
Ohm's Law Calculator)
the higher the voltage the higher the res. of the atty to get the same
vape .
The current power needed is around 7-10 watts , gotta do the math.
I could make up a chart of Volts vs resistance vs power that would help to make it easier.