No need to worry about charging batteries of your aiming device whilst on the field, the SPD Solar Combat Red Dot Reflex Optic available at Airsoft Atlanta solves that problem... "The SPD Solar Combat Red Dot Reflex Optic. Fits on standard top rails.  Solar powered to recharge its battery or AAA battery replacement.

• The SPD Combat optic has dual power modes; it can run off the Sun via the solar cell on top of the optic, or the onboard AAA Battery (included).
• Optic includes the Patented SwitchCover™ lens covers. PATENTS: US 9563050, CA 2881921, CN 201510067251, EP 2908084, PATENT PENDING
• Five brightness settings for the red dot reticle, in battery mode.
• Unlimited eye relief for flexible mounting positions on the firearm.
• Includes a low rail mount and a high quick release rail mount for mounting onto weaver/ Picatinny/ MIL-STD 1913 type rails. The base of the optic is compatible with most Aimpoint® Micro Mounts.
• US PAT. D900273"