Just to give you a quick lesson jmeklman, you'll need to know the voltage of the battery and it's max amperage and the resistance of the coil you'd like to use in ohms. Using ohms law (voltage/resistance=amperage) you'll be able to see the lowest coil resistance you can achieve given the amperage rating of the battery you are utilizing and then get a switch that can handle that amperage.
Example: in order to utilize a 20A 18650 with a nominal voltage of 3.6 volts, the lowest resistance coil you can utilize is .2 ohms at 64.8 watts and 18 amps (not hitting your 20amp max). Now, if you ran 2 18650
batteries in series (pos/pos neg/neg) of the same rating you can run a .4 ohm build (safer) at 129.6 watts (more power).
knowing the above information will help you find the switch you need. So, if you want to run an easy to find switch (6amps), you can run a .6 ohm build with a total of 6 amps and 21.6 watts.
Use
vapecalc.com to help you fine tune your build to get the optimum and SAFE setup.
As a reference for my typical build, i run a .9 ohm coil at 21 watts which utilizes 4.8 amps. That's on my single 18650 mod. Gives me plenty of battery life and the optimum vape for my tongue
But then again, I'm on a regulated mod.
If you are dead set on using lower amperage switches you'll have to do some research on MOSFETS. Some info can be found with a decent google search.
