Apple Watch Series 9 will not charge

The checks in more detail

A Series 9 with a depleted battery can take a few minutes to show a symbol. Heat stops charging, so move the watch somewhere cool. The Series 9's flat back with its sensors is easy to scratch, and a scratched or dirty back can reduce magnetic contact; check the puck sits flat. Force restart by holding the side button and the Digital Crown. If the watch charges on one cable and not on another, the cable is the cause. Apple Support can check a watch that refuses to charge on a known-good charger.

If the watch shows the lightning symbol in red, it needs to charge for a while before it can start; leave it on the charger for at least thirty minutes. A green lightning symbol means it is charging. If you see neither and the charging cable is plugged in correctly, try another cable and wall adapter. If the watch shows a charging symbol but the percentage does not rise after an hour, the battery or the watch's charging circuit may be faulty. If the watch has been in cold or hot conditions, it may refuse to charge until it returns to normal temperature, and it shows a thermometer symbol.

Wait fifteen minutes in a room-temperature spot and try again. Also check that you are using the cable that came with the watch, because third-party magnetic chargers that are not certified may not deliver fast charging or may not align properly with the Series 9's coil. Cleaning the charger's surface is a good habit: the magnetic puck collects metal dust that interferes with contact, and wiping it with a dry cloth removes it. If the puck is dusty or sticky, a gentle wipe with a slightly damp cloth, then drying, restores a clean surface. Avoid chargers that sit on a soft surface, as heat builds up under a watch on a pillow.