At Evike.com is the Matrix Icarus Solar Powered Red Dot Sight. If you are worried about losing power or running out batteries with your red dot sight, having a solar-powered one would ease your worries...  "Use the power of the sun the right way! With the Matrix Icarus Solar Powered Red Dot Sight.

Features:

• Solar powered design with built-in rechargeable battery eliminates the need to replace batteries; powered by sunlight or other light sources
• Adjustable windage and elevation
• Ruby coating reduces glare and provides a clear field of view
• Mounts to all 20mm accessory rails
• Aluminum alloy body provides superior durability

Oh, and it's a pretty darn good red-dot too!"