Battery only holds 4h instead of 8h

I have just bought a new Chuwi Larkbook X and I am really impressed with the quality.

But the battery life is really bad.
Out of the box it consumes too much power.
When I look into the c-States with HWinfo I can see that the package c-states are always at c2 which consumes too much power in idle. It should go to C6 or more.

Battery has only about 4h of battery life instead of 8h as advertised.

I think there must be a driver/bios problem that makes that.

Can you please provide a fix for that?