Your Kindle Battery should be fine for a short (few days) road trip. Be sure to bring your charger and charge it at night in the hotels. If you are going overseas and plan to be gone over a week, but less than two, make sure you carry your charger and any adaptors you may need for a foreign outlet.
If you need to get the most out of your battery on your Kindle, turn off the Internet access unless you absolutely need it at the time, like maybe once or twice a day. This can turn days of use into almost two weeks. You will be amazed. If recharging isn't as handy as you would like, this will help insure you have your books handy when you want them.
To turn off the wireless, press the menu button from the home screen. Toggle the 5 way and select wireless off. Turn it back on the same way (toggle and choose wireless on).
One of the largest battery drains can happen if you download several books at a time. Kindle has to index each book (that's why the search is so good), and this takes a little time, and quite a few battery resources. So any time you need to add a bunch of books at once, it wouldn't hurt to put your Kindle on the charger overnight, just to make sure it can recharge good.