Yeah I think I have the same issue. My battery would be at 100% then within 5 min it'll start dropping dramatically according to my FPV screen. Here's what my assistant software shows and I don't see any unusual things with this battery.
So the battery level threshold is clicked, at what point will the phantom automatically Go-Home?
View attachment 39914
It's suppose to RTH when it reaches a critical level but I never check that box simply because it work as failsafe. The Other reason is it could be under something when RTH is triggered and it does ascend very fast. I think you get the picture.