Hy! i am facing a bat battery issue some times during my flight. During flight i notice that current increses to 20A and as soon as current increase the voltage drops significantly and mission planner showing incorrect remaining battery capacity.
Here are the flight logs: 18.06 - Google Drive
The voltage and current in log 83 look perfectly fine. The voltage drop when current increases is normal.
You could have an old battery, it could be low C rating, or there could be problem with poor wiring and connectors. The motors and props could even be sized wrong for your copter or purpose.
Impossible to say more without pictures or more info.
You should definitely set these or the battery will just get worse:
BATT_CRT_VOLT,14.00
BATT_LOW_VOLT,14.40
He should be using the methodic configurator software and those parameters whould be set automatically for him.