To use your laptop in the car and pull power from the car battery, you will need a power inverter. In some cases, your laptop manufacturer will offer an auto adaptor, but the power inverter, which has a universal power plug could prove far more versatile and worth the money. The power inverter will convert the DC auto battery power into the right AC power your laptop needs. The power inverter will plug directly into your cigarette lighter and then will have an adaptor end which will let you plug your power cord directly to your vehicle.
You have options in terms of power inverters as well. There are two main types; modified sine wave and pure sine wave. You should check your laptop manual, or the support site to find out if your laptop will accept either kinds of AC power created by these inverters. In some cases, the power created by the modified sine wave doesn't work with laptop computers, so you don't want to spend the money and be out of luck!
When you begin shopping for inverters, here are some things to remember. Laptop computers, whether a new laptop, used laptop or refurbished laptop will require between 50 and 70 watts of power. Make sure you buy a power inverter that will provide more than the power load that you need. If you need to do this frequently, you should make sure to buy a quality inverter because it will be a better investment in the long run. Xantex makes a great power inverter, especially the StatPower PW-50 or 75 or the ProWatt 150. For frequent road-trippers the Simlex Power pure sine wave inverter is a great choice that will last for a while.
Obviously, your RV probably has the right power plugs you need to run your laptop. The bigger issue with an RV'er is going to be finding consistent internet access for reasonable prices, or better yet, for free! Many RV campgrounds are now offering high speed wireless internet so their travelers can easily connect. You can find many campgrounds that offer WiFi at RV Internet Access (rvinternetaccess.com) and at sites like RV Travel (www.rvtravel.com). If you are camping our on your road-trip, you'll also be able to find tons of resources online like WiFi Free Spot (www.wififreespot.com) and others. As long as you have your power and your laptop is wireless enabled you should be good to go!
Just because you are on the road, doesn't mean you have to be disconnected from friends and family. Make sure your used laptop, refurbished laptop or even your new laptop is ready for power and Wifi and has the memory to support your internet connection and you'll be connected in no time, wherever and whenever you want!