I had been flying my phantom 3 advanced from a fully charged battery took off as normal flew out to 1500m all good flew back to home position and landed,then took off again battery was at 40% at take off flew out to 130m and noticed phantom was just drifting on its own away from me(was in P-GPS mode) then got a warning (Propulsion output is limited to ensure safety of battery) panicked a little and hit RTH phantom turned to face home position and climbed to the 50m altitude i have set but just carried on drifting away,cancelled RTH and flew back manually and landed safely any ideas what happened would be much appreciated