Default [Q] Battery Problem!!!

Hello friends,
I have the Z8 watch (I like this watch).
I have this problem: after a full charge of the battery, I see the on the watch 100% for 2 days which then drops to 90% to 80% and then the watch turns off!!!
What should I do to solve this problem that it would be normal?

Thanks and have a good day,
Arie.