Hey olliem601,
We see that you're having issues with your battery life after installing the latest watchOS 7, and we'd like to help!
Are you still noticing this issue after 48 hours of updating your device? Once the update has been made, it can take up to 48 hours for the device to finish re-indexing all your apps and data, and that can consume more battery power.
If you haven't yet, please try restarting both your Apple Watch and iPhone by following the steps from the articles below:
You can find more information about the Apple Watch battery life here: Apple Watch battery
Also, you can check out the great tips that are offered to maximize your battery life from the article here: Maximizing Battery Life and Lifespan
We hope this helps!
Warm regards.