Where did you get the 4.2 volts? is that just a general safe spot to start or should i use the volts that is stated on the battery ex. my 18650 battery says 3.7v . Also how would i determine the battery's CDR yes im kinda noob haha
4.2 volts is the full charge voltage of a Li cell used in vaping.
3.7 is the midway or nominal voltage of the cell during discharge.
During cell discharge the voltage will gradually drop.
Most people recharge their cells at around 3 volts or a bit more.
Running a Li cell all the way dead or below 2.5 volts makes them somewhat iffy/dangerous to recharge.
Running a cell too low is one thing to learn about using mechs as they do not shut off like a regulated/protected mod will do.
I use 4.2 volts in ohms law calcs to give some safety headroom.
Actual operating under a load cell output voltage will be less than 4.2 volts though.
If running a single cell mech and drawing much current the actual under load output voltage will be more like 3.7 - 3.8 volts for a fully charged cell.
The guy that made the vids at the following link is pretty much the battery guru for US vapers and I strongly recommend watching some of his vids.
ALL mech vapers should watch his vids and even non mech users benefit from watching them.
https://www.youtube.com/channel/UCePHh3NMvu3rW2LFJeOWo-Q