Here the answer from Zero for this question.
"On page 1.8 from the Owner’s Manual you will find the parameters that might influence the range of the vehicle. However the experience that you describe below is basically not mentioned on that specific page. The power algorithm that is notice by the Customer is to prevent damage on the Battery, thus to perform correctly over the lifetime. This embedded firmware, the algorithm, allows the Battery to discharge quicker from fully charged to half way down. If the State of Charge (SOC) drops below 45-50% the power is cutting back. Although I don’t know all the ins- and outs about the algorithm, you will notice a significant drop in performance below the 30 %. Basically the algorithm protects the Battery from quick discharge at low energy level, to guarantee the lifetime. This is something I personally noticed riding a 15MY FX."
I had a long drive and drove first time down to 5%. This time I didn´t notice any power drop untill 50%, charger was plugged 24hr before this run and the previous run was just out of charger.
Zero is not gonna leave you halfway easy, there is no horry when you are under 30%
Now when I know this is normal behaviour I dont mind the power drop. Good thing there is solution for this, Quick charger is more significant thing to buy if I want to drive more with full power