Blank/black screen Apple Watch SE model

Hi, I have recently bought an SE model watch and it appears that once it gets to 50% or less battery the screen goes blank, so it will not wake up - whether this be on the setting for wake on wrist raise or wake on crown up.

It is up to date with the latest IOS, have unpaired it, and completed forced restarts. BUT every time it gets to below the 50% battery it is the same thing. The phone is still on, as I feel the vibration to indicate that I have a notification yet I cannot see it. The battery life is also very bad with just 8 hours back up and I think it may be linked to this issue also.

I am really struggling with this watch. Please help if any one know about this problem