When you say the laptop takes 16V @ 3.6 amps, you're talking about the utput of the charger right? You are going to have some sort of regulation in between the laptop and the lighter plug right? Like a 12V-ish -> 16V regulated charger, right?
If you don't have any regulation, between the laptop and the car's electrics, you are going to be in the market for a new laptop very soon. This is of course, unless the laptop has built in regulation, but I seriously doubt it.