@Mhutch: That's certainly not what we'd expect from a brand new Galaxy Watch Active. If you charge the watch to 100%, use it as you would normally until it reaches 50%, then head to the Galaxy Wearables app on your phone > About Watch > Battery, can you see any apps or features listed here that are using a higher than average amount of battery?
In the meantime, while in the Wearables app, head to About Watch > Update Watch Software > Update Now to see if any updates are available that might address the situation. You may also wish to try enabling Power Saving on the watch by heading to Settings > Battery > Power Saving > Tick while you're in bed to reduce the amount of background activity. If you have installed any apps on the device, please try disabling them temporarily to see if you notice an improvement. Let me know how you get on.
