If you change the battery every few years.. there is no reason to ever have an issue in the field. I have 4 Burris FF3.. I hunt a lot.. and only change the batteries every 2 or 3 years. I do carry a spare in the vest, but never needed it. I'm sure they would last 5 years. Just make sure you use the Duracell battery when you change them.. others have had issues trying to get the cap screwed down with different battery brands