There seems to be repeated threads of the H falling out of the sky and the culprit may possibly be the battery was not inserted fully and did not 'click' into the locked positon. I have had this occur - but was saved by this simple solution with Velcro. In my case, I removed the Velcro and the battery slide out as I picked up the H after landing. I believe the battery would have slide out during the flight if not for the Velcro with the result being the H in the Pacific ocean.
As a side note, all the prior kit drones I have built Velcro was used as the primary method to hold the battery; this includes heavier 4S and 6S batteries without failure.
This is a bit crude, but is very effective. I can pick up the drone by the battery tab without the battery in the clicked position and carry the H around.

As a side note, all the prior kit drones I have built Velcro was used as the primary method to hold the battery; this includes heavier 4S and 6S batteries without failure.
This is a bit crude, but is very effective. I can pick up the drone by the battery tab without the battery in the clicked position and carry the H around.
