Help with charging laptop while driving car?

most laptop power bricks need either 110/220v ac. and the average car electricity is either 12/24v dc. so you will need an inverter to convert the dc current into ac. mind you that these inverter still seeps power from your car's battery and your car's battery is charged via a thingy called the alternator. so if your car's alternator is not big enough to cope with the power you draw via inverter, you'll drain the battery(even when the engine is running), drain your battery often enough then' you'll never need to work out again since you'll have to push your car to do a rolling start. bigger inverter needs to be wired directly to battery since it will melt your cigarrete lighter socket, not to mention they're big and heavy and takes some place in yhe cabin (you cant hide it without airflow since it will need cooling).

the power rating for inverter can be roughly calculated using your laptop's max power draw. there's a voltage rating and an amper rating written on the power bring. example. your powerbrick need 110v ac and can deliver 10ampere of 20v dc.
so it will draw roughly above 10x20= 200watt. for efficiency issues (efficient inverter is VERY expensive) you should add 30-50% from the power you needed. in this case it's youll want 360-400 watt typical/continuous inverter.