AppleWatch 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 Apple Lithium-ion Batteries website.
Set up the charger
For best results, charge your AppleWatch with the included magnetic charger. You can also use the MagSafe Duo Charger or a compatible third-party charger (sold separately).
In a well-ventilated area, place your charger on a flat surface.
Plug the charger into a power adapter (sold separately).
Plug the adapter into a power outlet.
Begin charging AppleWatch
If AppleWatch needs to be charged, the low battery symbol 
appears on the screen.
Position the back of your AppleWatch on the charger. The concave end of the charger magnetically snaps to the back of your AppleWatch and aligns it properly.
AppleWatch plays a chime when charging begins (unless your watch is in Silent mode) and a charging symbol
appears on the watch face.See AlsoProtect a lost Apple WatchNote: If the charging symbol is yellow, AppleWatch is in Low Power Mode. Low Power Mode turns off when the battery is charged to 80%.
appears on the watch face.Optimize battery charging
To reduce battery aging, AppleWatch uses on-device machine learning to learn your daily charging routines so it can wait to finish charging past 80 percent until you need to use it.
Go to the Settings app
on your AppleWatch.Tap Battery, then tap Battery Health.
Turn on Optimized Battery Charging or Optimized Charge Limit.
on your AppleWatch.About fast charging
Fast charging requires a compatible charger and an 18 W or greater USB-C Power Adapter. See the Apple Support article About fast charge on AppleWatch.
Note: Fast charging isn’t available in all countries or regions. The specifications of the included magnetic charger may vary depending on your country or region. For information about fast charging in China and Indonesia, see this Apple Support article.
WARNING: For important safety information about the battery and charging AppleWatch, see Important safety information for AppleWatch.
