All bought used ....... i have 4 batteries marked 1 to 4.when i fly 1 and 2 all is good no probs and everything works as it should.when i use 3 and 4 everything works great rth, fail safe, direction control, altitude ect, but i have drift in the wind. maybe 10m and then it tries to hold for approx 1-2 seconds then drifts again and goes on like that till out of range.reinstall 1 and 2 perfect again.i have noticed that there are serial numbers on 1 and 2 but not 3 and 4. all are recognised in the assist yet there are different firmwares 1 and 2 have 2.0.0.0 and yet 3 and 4 have 1.0.0.9....and no update avail.so are these off a eariler system or copies.cheers