Low battery indicator doesn't work on batteries but works with trim
Put a pull-up resistor of 10 K from the pin 1 to VCC. LM393 has open collector output, cannot drive high by itself. 

Later edit , the battery voltage is arround 4V which is out of the common mode range of LM393 with 5V supply (0..3V). Use a divider like in the schematic below or use the 100k pot that you used for tests to bring the voltage in the allowed range. 







simulate this circuit &ndash; Schematic created using CircuitLab