It's likely a CR2032 battery, get three for $1 at Dollarama, or two for $8 at Walmart.
Oh wait, my brain farted, was talking about the battery, quarter sized, for a lot of scopes, in my brain I thought Tasco Aimpoint, is actualy Tasco Red Dot. Ignore, but the batteries I mentioned ARE found in a lot of auto remotes, garage door opener remotes, scopes and sights, etc. So the good info still stands for the record.