Whats the highest watts you can run in your truck, using a power inverter? I wanted to get a power inverter for my truck, to run a laptop, and maybe a portable printer for job estimates.. Just wondering, does the larger ones rundown & kill the trucks battery faster? And whats the most you can have? Is a larger one really needed? If my laptop is only using 100watts, do i really need to buy a 1000watt one? How do you know how many watts your battery can put out? Thanks guys..