Even with a full charge a critically low battery warning during flight will cause the drone to land where and when. I've had to climb fences..etc..for that very reason.
Hello from Engie I have had similar problem battery shows fully charged but as soon as I start the drone I get low battery signal, stop drone battery still shows 4 green lights ,my problem is battery is buggered. This could be your problem, hope this helps . Best regards Engie.