How to customize/control battery power in jMAVSim

Hello guys,

I wonder if there were any ways to customize/control the battery in simulation.
My situation :

But during the flight, battery power goes down to 51% and stop there. No more decreasing at all.
Could you please tell me how to change this value or control/customize battery power in this case?
I have to modify in QGroundControl parameters or make changes in Firmware source?

Thank you very much,
Wish you all the best