SPD Solar Red Dot Reflex Optic w/ Locking Quick Release Picatinny Mount - BlackSPD has a dual power source. The Red Dot reflex optic can be powered by the sun via the top mounted solar cell or the included AA battery. Solar cells mounted on top of the reflex sight will power the red dot whenever there is sufficient sun light on the solar cells. The Red Dot automatically turns on when there is sufficient sun light. The SPD Red Dot can also be powered by the AA battery. AA battery should be used when there isn't enough sun light,