Hello and welcome to Apple Support Communities, BigBadPhil!
We understand you've noticed that your battery doesn't last as long as it used to. We'd be happy to help you out with this.
On your Apple Watch, go to Settings > Battery and check the Battery Health. You can also use the steps here to learn how to get the most out of your battery:
Apple Watch Battery and Performance - Apple Support
"How to maximize battery performance
“Battery life” is the amount of time a device runs before it needs to be recharged. “Battery lifespan” is the amount of time a battery lasts until it is no longer useful. One factor affecting battery life and lifespan is the mix of things you do with your device. No matter how you use it, there are ways to help extend your device’s battery lifespan. A battery’s lifespan is related to its “chemical age,” which is more than just the passage of time. It includes different factors, such as the number of charge cycles and how it was cared for. Follow these tips to maximize battery performance and help extend battery lifespan. For example, keep Apple Watch half-charged when it’s stored for the long term. Also avoid charging or leaving Apple Watch in hot environments, including direct sun exposure, for extended periods of time."
Have a great day!