Under the previous App, if you started a fight with less than a full battery, you ran the risk of the app saying the battery was drained, and it would try to land. Happened to me several times. I would powere back on like you, and would have battery power.
Solution: upgrade to newest firmware. Always start with a fully charged battery. "Start" is the key word. You can start/stop flights on the same battery, but when you put in a new one, it needs to be fully charged. I have had no further issues since using batteries in this manner.