A low battery indicator board that uses two transistors and a 10k trim potentiometer to set low battery voltage. When the battery voltage is high, Q2 is active, allowing current to flow through. The current flow brings the base voltage of Q1 to 0V, with Q1 subsequently not being active and the LED is not switched on. When the voltage on the base of Q2 is lower than 0.7V (given by the output of the voltage divider on R4) Q2 is off. The current flowing through R2 thus goes only into the base of Q1. Q1’s base is now at a voltage higher than 0.7V, which activates Q1 and turns on the LED, indicating a low battery voltage.