Ok, the information i gave is from multimeter. Multimeter measures in some interval and returns the average value, which in case of square wave with pick at 8.9V and fall to 0V is about 4.5V.
Today i did measure with oscilloscope. The output of the device is 33.8kHz perfect square wave (with sharp edges) between 0V and 8.9V. I also measure the same at the output of the device and once at the handlebars. It was the same, even i didn't use copper handles.
So, when measuring with multimeter is normal to have half of the actual voltage.