The battery life of my Apple Watch Series 9 is short

If your Apple Watch uses too much power and the battery life is short, there may be several causes of the problem.

Recalibrate the battery by following these steps: 1. Fully charge the battery and leave it to charge for an additional two hours. 2. Disconnect your Apple Watch from the charger and then drain the battery completely. 3. Connect your Apple Watch to the charger again and fully charge the battery. If this doesn't help, you can wait for the next software update, which may resolve the issue.

Go to the Apple website to see if it's possible to change the battery.