Hi, I have a newer Dell Inspiron laptop.....I like to go off-road for 2-3 days at a time, and I need my laptop to use during that time (I'm a writer.) You can't switch out batteries on it....so I'm wondering the best option for recharging it a few times. I can always charge it off the car battery w/my ac/dc converter, but I hesitate to run the car at idle for 1-2 hours. What's the best option? I'm assuming it will be a powerful portable charger?