US18650S: SONY brand 3.7v Li-ION rechargeable battery 18650. Size: 2.53" long x 0.712" diameter. Available plain for $4.00 each, or with Solder Tabs for $5.95 each. These are "raw" cells; they do Not have a protective circuit board. Extreme care and caution must be exercised when working with these type cells.