Apple Watch has an internal lithium-ion rechargeable battery. Compared with traditional battery technology, lithium-ion batteries are lighter, charge faster, last longer, and have a higher power density for more battery life.
To understand how your battery works so you can get the most out of it, see the appears on the watch face.
Note: If the charging symbol is yellow, Apple Watch is in Apple Support article.
WARNING: For important safety information about the battery and charging Apple Watch, see Apple Support article: If your Apple Watch won’t charge or it won’t turn on