Hopefully you guys can help steer me in the right direction. 2 times now, my Phantom 2 has been in the air, plenty of satellites connected and home lock was fine, all of the sudden it starts losing altitude fast even though I am pressing the controller full throttle up. I have a Phantom 2 non-vision and everything on it is stock. I have now had this happen to me twice and the only thing consistent in both crashes was the batteries hadn't been charged for a few days so they weren't full but had at least 80% charge on launch. The first time it happened I was leaving Breckenridge, CO (high altitude and a little cold out) and wanted to take a quick video of the sunset. I set everything up as usual, calibrated the compass, GPS and home lock all good, battery was around 80%. Launched it straight up and it would only go up to about 30 meters and then stopped regardless of having full throttle up. Obviously something was wrong so I decided to just let it hover and spin it 360 real fast to get a shot and then planned to bring it down. About midway through the rotation it just started to fall from the sky, barely responsive to the controller but I managed to direct it close enough for me to soften the blow to the ground. Damage was minor breaking one prop and damaging another. Took it home, pulled it apart, nothing looked damaged. Swapped out all the props for new ones, hooked it up to my computer and did every calibration, Adv. IMU as well. Fast forward a few months, had flown it a handful of times in between with no issues. I was out at a festival and decided to do a fly over of the whole event. Set up as normal, compass calibration, GPS and home lock. This time the batteries were displaying around 90%. The first launch went fine flew around everything getting some great video until I realized I forgot to hit record, so I brought it down, everything nice and good. Swapped out the battery so I could have a long enough flight time, battery was displaying around 90% as well. Hit record this time, launched it, did a nice little fly around and was circling the event. It was about 60 meters away from me and about 40 meters up when all of the sudden it starts losing altitude fast, I am jamming up on the throttle to no avail. It still responded to my other stick inputs so I was able to steer it away from any people but it came crashing down into the side of a tent and into tall soft grass. No visible damage this time, it seemed to be a soft enough crash. Both times I have had full GPS and home lock, at least 9 satellites connected, and compass was freshly calibrated before launch. Could this all be because of not having full and freshly charged batteries? Both times the battery level was displaying over 50% when it went down. Any help or direction toward more diagnostics would be extremely helpful. I am at the point of not feeling safe about launching it in any place that might cause a more serious crash or injury to someone. Thanks.