Good thought, but unfortunately it is not that simple. I measured the lipo to 7.8V, which is normal for a 2s. The ECU is also set for lipo mode. If I unplug the "phone cable" between the turbine and ECU the GSU displays the right voltage.

The ECU definitely accepts higher then 7.6V as it is made for 2s lipo (meaning up to 8.4V should be ok)