I went back again to the same spot and did another range test. The wind was only 4 knots, but this time I had a headwind on the way back. Gentle breeze into the lake made the lake super flat and wi-fi signal to carry at maximum range. I have noticed waves on the lake change signal profile quite a lot.
S Mode and full gas straight. I knew where cellphone towers are and stayed as far from them as possible. 10m above the water to be able to use water as a wi-fi reflector.
I got to 4km mark and almost got paralyzed when I saw a message: low battery "return home"

I pressed yes because I could not see how much battery I have left (white font on white sky = can't see it). AC stopped and slowly started to increase elevation to 30m and then slowly went back, and this took good 40 seconds before it was at speed going back, what I waste of time! I was so scared I forgot simple math and thought I would miss home by 200m. I was already thinking to order another AC as a replacement. On the way back still in sports mode full gas last 3-4 min I had constant message "Aircraft power insufficient", and speed dropped to 30-35km/h I think batteries had a hard time to keep up.
Since video transmission was not interrupted, I'm pretty sure it would go further. This was my last test; it is just stupid to go that far, too much stress and I just see no point.
Few tips for curious types:
- No matter what, check the wind and ALWAYS make sure to have a tailwind on the way back; this way, you will help your batteries and achieve longer results.
- DO not use return home; it just takes too much time. If you can't come back without RTH just don't run the test, I could manually turn back in 2-3 sec instead of 40s.
- If you are doing the test over water waves, make a big difference.
- The last tip: don't do it at all, it is not worth it, it does go to 4km what's the point?
Here is a video: