OpenCat.ino non-stop check battery

I assembled Bittle as per instructions, but got blocked at uploading of OpenCat.ino https://bittle.petoi.com/6-calibration#6-1-3-upload-opencat-ino

I see following and not stopping.

Battery , Servo are connected to the board.

* Start *
Initialize I2C
Connect MPU6050
Test connection
MPU successful
Initialize DMP
862 122 6 -5 
Enable DMP
Enable interrupt
DMP ready!

* Assigning 2 skill addresses...
1
Finished!

check battery
69.00
check battery
31.00
check battery
17.00
check battery
9.00
check battery
4.00
check battery
1.00
check battery
0.00
check battery
0.00
check battery
0.00
check battery
0.00
check battery
0.00
check battery
0.00
check battery
0.00
check battery
0.00
check battery
0.00
check battery

What is this check battery ? how can I fix this ?