Energizer CR2450 Lithium Coin Battery 1pk

The CR2450 is the large coin cell, and a lot of gear runs on it: red dot sights, enclosed reflex optics, some weapon lights, rangefinders and electronic muffs. This is Energizer's 3 volt lithium version, with the long shelf life that comes with lithium chemistry, so a spare tossed in the range bag will still be good years from now.

One cell per pack. If the optic is riding on a defensive rifle or a carry gun, change the battery on a calendar schedule instead of waiting for the dot to fade, and keep the old cell as a backup for something that matters less.