Battery madness

I have a Tarot 690, 750kv hex with m8n, ardupilot 2.8apm. Running 3s 8000 mah Floureon bats. The thing is set in Mission planner to go into RTL at 10.2 but is RTL landing at 11.7 . Does the laptop have to be on and connected or is there another reason this would happen both batteries. I take it to manual and can hover with plenty of power for 10 minutes easily. Also I have everything to run both parallel would I see double flight time or does battery weight cancel out the other 8000. If I get 15 minutes out of 3s 8000 would could I expect out of 4s 24,400 mah? Thanks Running Radiolink at10

Should have said I can run 10 minutes additional, it takes 2 or 3 minutes only you hit RTL coming back with the alarm on the balance lead quiet but RTL is way too soon

You will need to supply some logs for anyone to ascertain what is going on.

Without log file my guess would be you are trusting the voltage reading of a power module mounted in the usual way, ignoring physics.

Does anyone know anything about the Floureon Lipo Quality?

have you calibrated the power sensor?

you may be seeing voltage sag in the lipo, ie in flight the pack voltage is hitting 10.2V, but when measuring on the ground (under no load), you are seeing 11.7V or higher

I have not calibrated the power sensor, I will give that a shot thank you