With fast charge, the battery level on Apple Watch Series 7 and later can go from 0 percent to 80 percent in about 45 minutes. The battery level on Apple Watch Ultra can go from 0 percent to 80 percent in about an hour. Fast charging requires an Apple USB-C Magnetic Fast Charging Cable. You can identify this cable from other chargers by the USB-C connector and the aluminum around the magnetic charger. You also need one of these power adapters: Apple 18W, 20W, 29W, 30W, 61W, 87W, or 96W USB-C Power Adapter. A comparable third-party USB-C power adapter that supports USB Power Delivery (USB-PD) of 5W or greater. Fast charging might not work in conditions that are too cold or too hot. If you have enabled cellular capability on your Apple Watch, keep your paired iPhone within range of your Apple Watch when fast charging.