My Apple Watch drains in 2 hours while using the workout app. It used to be able to handle 3 or 4 times that time

Watch uses a LOT of battery 

Make sure to turn off background app refresh and  check walkie talkie is not accidentally turned on.

Check there is no workout running (yellow circle at top if screen.)

Make sure you have no VPN or VPN based ad-blocker on the iphone. Uninstall it then remove any profiles (iPhone Settings, General VPN & Device Management)

Force restart your watch i.e. press and hold both the side button and Digital Crown for at least 10 seconds, then release both buttons when you see the Apple logo. 

Then while the Watch is restarting Force Restart the paired iphone   Force restart iPhone – Apple Support (UK)

Try it for a couple of days especially if you sync photos to your Watch.

If the battery still drains  then Unpair the watch and then pair it again. 

Unpair and erase your Apple Watch – Apple Support (UK) 

Set up your Apple Watch – Apple Support (UK) 

More info

Apple Watch - Battery - Apple (UK)

Batteries - Maximising Performance - Apple (UK)

Then if still no better you can check for damaged or self-discharging battery... 

How to check your Apple Watch battery fo… - Apple Community

 If it still discharges after all Watch resets try this user tip

Apple Watch battery drain - the ultimate … - Apple Community

It is possible the battery is below capacity. Check Watch, Settings, Battery, Battery health us 80% or better.

Also

How to check your Apple Watch battery fo… - Apple Community

It looks like the low power mode us on during workout (yellow) but the steep stepped slope is unusual

You might try the fewer heart readings

(I assume it passed the overnight power-off test. Even batteries with 92% capacity can leak)

Thats great, glad I could help.