Pixhawk Dronekit Python on Raspberry Pi3 Error with Battery

I’m using the Pixhawk and Raspberry Pi3 with Dronekit Python.
When i’m connecting with Battery, everything is working fine and suddenly after one reboot, with the Battery, the dronekit is not working. It’s showing
Exception in message handler for HEARTBEAT
mode 0 not available on mavlink defnition
Link timeout, No HEARTBEAT in last 5 sec

I’m using the Telemetry 1 port for Raspberry Pi, and connected with /dev/serial0 baud 57600

When i’m using the external power supply for the pixhawk, it doesn’t have a problem, connecting and communicating perfectly. still the problem with battery connection

i have tried different LiPo batteries, but issue not solved.

Troubleshooting ideas are appreciated.