You have to carry extra batteries but having them lose in your gear bag or backpack is a bad idea. to see a step by step guide on how to properly carry your batteries.
TIP: Did you know a cold battery doesn’t work as well as a warm battery? If you are out in winter, keep your extra set of batteries in a clothing pocket close to your body to keep them warm. If you find yourself without a back-up set of batteries and have a “dead battery” warm it up by putting it in an inside pocket of your clothing letting your body heat will warm up the battery. Re-install the battery and you might get a few more minutes of life out of it. I’ve resurrected many a camera battery this way.