I was just starting my flight today when about 400 ft out got a "warning: battery error, land as soon as possible" . Very very scary. Brought the bird very quickly back and landed (was up about 100ft) . When inspecting the drone I noticed the battery was slightly pulled out. I then remembered I showed the battery to a friend today and probably did not push it all the way in after that. I pushed it firmly in, did some more test flights which were perfect and had a big sigh of relief. So - a very stupid mistake on my part, and thank God to the advanced technology which had the ability to inform me the battery was dislodged. Note to self : always check battery sits tightly inside.