tuning in car

So I'm about to start street tuning my car. My battery does last a good 2-3-4 hours on power saver mode, but the screen is very dark and hard to see unless its night time. And on full power/even a balanced power program, it still eats up batter in just over an hour. Mainly only a problem if the battery isnt 100% Either way its just 10x easier to have constant power so:

Should I be normal, and get a 12v > 120v power supply, then use my normal 120v wall charger for the laptop?

Or is there a GRM solution that doesn't change voltage ranges and phases twice for almost no reason?

~Alex

I bought an inverter to run 120V in the car to run TunerStudio on my old old laptop (battery lasts 7 minutes, but laptop has a serial port in it). You'll probably need at least 300W to feed the laptop. This has worked super awesome for me.

Power output should be labeled on the power brick for the laptop, and then figure on, what, 80% efficiency? Switching supplies are fairly efficient. My Apple laptops use 85 watt or smaller power bricks, I think my old Compaq (with both serial and USB ports so I keep it around for projects that so far never come along) was 50 watts or so. You shouldn't need much for an inverter to drive a laptop.

Another vote for inverter. An el-cheapo one from Amazon powered my MacBook Pro just fine when I was putzing with my MegaSquirt...