I started losing pics on my M60 when I got to 35-40% battery. I know I was losing pics because I was sitting in my stand watching the deer in front of my cam but they weren't on my card. I read on some forum to never leave a Moultrie in the field with less than 30-35% batteries when it freezes at night. Well my nights are now down to the 20's so I figured I would change them when the Cam was at 38%. Depending on your weather you may get some more life out of 40% but you'll never know without another camera next to it.