check battery health of apple watch

Three hours isn’t very long unless you are accessing it a lot - listening to music, playing games, etc. It would help us if you told us how old your watch is, battery life degrades with age, and what apps you have installed and use frequently. Also, I had an issue with my first Apple Watch that I fixed by unpairing it and resetting it. I honestly don’t know if I really had to go to that extreme to fix it but it did resolve my short battery life. How to reset an Apple Watch: Unpair and erase your Apple Watch - Apple Support

The watch is at least 3 years old now. When new, my AW4 went from full charge to about 20% during a day’s use and maybe down to 50% on weekends. Over a 3-5 year lifespan that’s a lot of recharge-discharge cycles which is what defines the life of a modern battery. My battery required replacing after about 3 years. I suspect you are at that point now.