My robot works just fine when tethered by its USB to my PC. I can issue commands from my cell phone (terminal mode) to the robot and they are transmitted and received via HC-05 bluetooth. The robot has two 9V batteries wired in parallel that currently have 7.65 volts (in line voltmeter) and power the L298N H-Bridge. The VCC output from the H-Bridge provides power to the Nano.
When connected VIA USB, diagnostic output is transmitted over the Serial port back to the PC which displays this information. When I disconnect the USB, the robot, LED 13 on the Nano and the power LED on the H-Bridge are still lit; however, the Bluetooth connection is lost and the HC-05 starts its rapid blink.
My goal is to be able to run the robot autonomously, but I am a bit stuck here. I have two questions: 1) How do I diagnose what is happening here? 2) As a general rule, when running the Nano off battery power, what might be causing it to fail?