I run rechargeable AAs in my cams year round and my impression is they really shine in colder weather compared to hotter, but they hold their own in all temps (25-90F). I usually let them run 4-6 weeks at the longest interval, regardless of the time of year. I only use Sanyo Eneloops and Maha Imedions and have been completely satisfied over the last 4-5 years. Furthermore, I have not had to purchase any batteries during this time either. My sunk cost up front was a fair amount, but I feel as if they have paid for themselves at this point.