Hello Sir!
As long as the battery is below 65%, You have absolutly nothing to fear..
I have attatched a file of the manual, and it seems like the P3S' discharge function stops at the point of 65% :)
Okay i get your question, If the fpv will work with that specific setup. And i think it will..
Running with that setup myself, and thinking about gering the fpv ASAP (: