What kinds of batteries do smartwatches typically use?

Smartwatches typically come with lithium-ion polymer (shortened as Li-Po) batteries. Li-Po batteries are also commonly used in portable devices, such as smartphones, digital cameras, tablets and handheld game consoles.

For example, the 38-millimeter Apple Watch uses a 3.8V, 0.78Wh built-in rechargeable Li-Po battery, and the FitBit Surge uses a Li-Po battery as well, which is believed to be the 4.35 V BQ24232H lithium-based battery from Texas Instruments. Lithium-ion polymer battery is a rechargeable battery of lithium-ion technology. The principle of lithium-ion technology is the movement of lithium ions from the negative electrode to the positive electrode during discharge and back when charging. Li-Po batteries in smartwatches and portable devices often come in a pouch format; hence, they is lighter and less rigid compared to batteries that are in cylinder or prism shape.