The standard voltage is generally between 4v and 3v. With
batteries you generally see a ~Xv because it’s nominal voltage. (More or less the average).
batteries are a bit like balloons. 5v is within spec. Which is handy as that is what usb puts out. Up to 9v can be done ( effectively a 2 battery mech mod with fresh
batteries) but steps need to be taken to reduce the heat. Generally a shorter or thicker wire to reduce resistance. You’re effectively building an RDA that uses pure VG (which is what stage smoke machines use). Numbers can be found in mech mod descriptions.
Some sort of wicking will generally be needed to get the VG to the wire. Cotton is traditional with RDAs as it acts as a fuse. If it gets too hot the cotton burns and it stops bringing VG to the heating element. More heat resistant substances can be used though (glass fiber is common) which never burns allowing the coil to potentially get VERY hot. The upper limit is then the melting point of the metal the coil is made out of rather than the 451f of cellulose. You can use no wick at all and run the wire through the liquid container itself. The liquid then acts as a coolant and you get bubbles, which may be wanted. Doing that requires resistance/no resistance wire though (as you don’t want the resistance wire to touch and melt the container) which is a pain to make. You need to weld the two wires together end to end. This can be done using a home made spot welder that uses a capacitor as the power source. Mostly it’s just an easy way to get a switch, a power source, and a capacitor the right size from the flash mechanism. There are also links to calculator apps for Resistance ohm rating of given thicknesses and types of wire.
