When I use my Galaxy Watch Active as standalone, the biggest battery consumer are Watch faces and Samsung health with 29% and 14%, respectively, but my watch still manages to reach ~8 hours with 13% left. But when I connect it to my Note 9 the entire time, the biggest battery consumer is Settings with 14% and reaches 13% battery in just 3 hours. I already tried resetting the watch and the phone. I already reinstalled the Galaxy Wearable app. The same case happened with my Galaxy Watch. 25% in 7 hours, but it has bigger battery.
I am sorry you have tried all the troubleshooting steps to get this issue solved with your watch and the problem is still re-occurring.
My suggestion is to call 1800-SAMSUNG (1800-726-7864). Once you call them, try to reach a representative and have the valid proof of purchase handy and the serial number of the device. Let them know you want to mail in the watch for service and they will email you a UPS shipping label and give you the proper instructions on how to do this process. It typically takes 7-14 business days for you to receive them back. The serial number/IMEI and the proof of purchase is typically what is needed as long as the device was purchased less than a year ago. If it has been more than a year, there may be an out of warranty charge and this will all be explained in the phone call. Try to be as specific in the phone call and be aware that they will ask you for a shipping address.
If you have any questions, please let us know.