Yes—bringing at least one spare CR123 is a good idea. Battery life depends on how much you shoot and how often the camera uses power, so there isn’t a fixed trip-length answer. For a 20-day trip, a fresh battery may last the whole time, but carrying a backup is the safest option so you don’t get stuck with a dead camera. The good news is that CR123 batteries are common enough that you can often find replacements while traveling if needed.