Battery calibration not working !

So i have my Steamdeck since the beginning and my battery was never top.
It shows battery health at 97% however the last year or so whenever i hit +-50% the remaining 50% drains very fast.
In about 15 minutes or so the steamdeck shuts off. (idle)

However, after it shuts off in steam i can enter bios mode without the charger and it'll remain on for at least 20-30 minutes ...
I tried draining it completely multiple times now and letting it recharge for more than a day but the issue remains the same.
Perfect battery health but at 50% it dies very fast even if it still keeps working in the bios.

Anyone has the same issue and knows what to do ?
I am not technical, i do not see me change the battery, especially since it's the LED model and the battery is glued in tight.

At the moment i am draining the battery again in the bios and it's still on for about 20 minutes now even if it was at 1% in steam. (it shut off before but i restarted and then it displayed 1%)

Also i keep setting the clock correctly in the bios but when i save and it reboots it is again two hours behind.
I suppose it's perhaps normal ? In steam it's ok, i assume it takes the clock from the internet connection.
Other bios settings are perfectly retained.

Many thanks.