I am in a similar situation and am in the final stages of testing my laptop carpc setup. I am using this adaptor (http://www.maplin.co.uk/Module.aspx?...ldID=&doy=6m12), i'm planning on removing the cigarette lighter plug and re-wiring it into the car's ignition live circuit. The laptop will then always be on charge when the car is running. I have set the powersave options on the laptop so that the system goes onto standby after 1min when running on battery. I have found that the battery will last several days with the system on standby, and will commence charging again when I get back in the car and turn the ignition on. Also solves getting fast boot times, as my laptop returns from standby in less than a second when i tap the touchscreen after turning the ignition. As long as the in dash touchscreen and amps will run of ignition live as well i hopefully shouldn't need a startup/shutdown controller. I'll let you know if i get any problems.