For me the battery lasts 1.5 to 2 days at least. I am not an avid sporter though.
To improve the battery life, you could try the following options -
1. Reduce the screen brightness, especially when you are indoors
2. Turn off Always on display
3. Turn on Wifi, GPS and NFS only when needed
4. Turn on Battery saver option
5. Have a look at the battery usage of the apps in the Wear app --> Settings --> Battery
Hope these help improve the battery life of your watch.