For anyone who has purchased a smaller sized 18650 battery, you can use a nylon spacer on the negative side to increase the size by 1/8”. Simply use electrical tape to secure them. It becomes the same size as the Ring battery. You will have to extend the spring slightly on the negative side of the battery compartment with some needle nose pliers. This has worked well for me so far. I have 20 lights. I had purchased some Skywolfeye batteries for a far better price than the Streamlight or SNSYIY. The nylon spacer can be found at Lowe’s Item #423470. The size is .505x3/4”x 1/8”.