Dion, Good luck. My attempts to make a vaporizor in the last few years have required a great deal of bypassing fancy electronics and were far from simple. I suspect that making one with a MODERN battery charger is well beyond most people. I am not going to attempt it again.
The problem is MODERN battery chargers have a lot of electronics built into them that are designed to disable the charger if you short the outputs. When you make a vaporizor you are shorting the outputs. So, you have to defeat or remove these electronics. But, they make things with as few parts as possible. Thus bypassing or removing only some of the electronics is not possible. You have to rewire everything from scratch. To do this you need to really understand how rectifiers work, etc.
Its like cars and trucks. 40 years ago, they hard distributor and points. You could work on your own car. Tune it up. No more! Now you need hook up your car to a fancy computer. You can't do it yourself for a reasonable cost.
I now recommend people get the "Burnmaster" unit made by Woodcarvers Supply. It gets hotter than anything else.
Carl's take on the best Woodburners, Tips, & Books for woodturners. What he recommends for his students.
carlford.us
Note: I live in New York state. In NY all batter chargers you can purchase now have electronics that detect a short and disable the charger. Is this only NY state? I don't known. You many be able to find a simple one in other states. But, probably not. Manufacturers like to make products they can sell in all 50 states.