If your watch battery is not lasting a whole round (especially on older generation of watch), there are a few things you can do to optimize battery usage. The key is to turn off sensors that you do not need, which tend to consume the most battery.
First of all, turn off the heart rate sensor. A golf game is considered a workout, and Apple Watch turns on the heart rate sensor by default. If you do not care about measuring heart rate while playing golf, go to the Apple Watch app on your phone, in the first tab, find Privacy->Motion & Fitness->Heart Rate, and turn it off. See screenshots below. This can typically save 50% of your battery, so we highly recommend it.
Beyond that, you could turn off motion sensors, which we use to track your golf swings. There are several ways to turn them off, in increasing power consuming order:
Since 2020, the "Lower Power Mode" also turn down the GPS update frequency, it will lower your battery consumption a lot. So we highly encourage you to try it, even in the "Simple" mode. The tradeoff is that when you raise to see the distance, it may take a few minutes for the accuracy to increase. Please wait for the "Accy" indicator on the watch to decrease before you can trust the distance number.
At the end of your game, you must terminate the session for the motion sensors to stop consuming battery. If you see the green workout icon on top of your watch, the workout session is still on, and the motion sensors (if used) and GPS are still consuming your battery.