Weird apple watch battery behaviour???

My Apple Watch series 4 battery is behaving rather strangely. Not only does it die at around 5-20% (sometimes as high as 30), the battery plummets quickly (around 8 hours of battery life). Sometimes however, the battery stays at 100% for almost 3 hours, then proceeds to decrease at the same rapid rate mentioned previously. As indicated in the first image.

I assumed with the second piece of evidence that the battery wasn’t being fully charged and the indicator was reading a false full charge (hence, staying at 100% for so long) and I always pop my watch off the charger when it’s full and wear it until it’s low or dies usually even over night. I decided to test the theory by leaving it charging all night, yet all that happened was the normal battery drain.

The image above is the result of that.

i have taken basic procedures, from hard reset to wiping the watch and restoring backup. I’ve deleted all apps that may be suspect to battery drain (ie noise or cloud battery) and have turned the brightness way down and it still drains pretty quickly.

Also, when the watch dies and enters the low power state, the low power indicator sometimes shows without the time, and showing the winding Apple Watch cable with the red low power symbol instead.

Does anyone have any explanation as to what’s going on? Thanks