The Photons use lithium batteries. Among other benefits, lithium batteries store very well. Manufacturers usually quote a 10-year shelf life, which I think means something like they have 90% of their original power after 10 years. Doug recommends a conservative rotation schedule that I think is about 4 years. Personally, I would be comfortable going out to the 10 years (based on my individual needs and risk tolerance).<br><br>