1. First of all, please make sure the batteries work well and installed correctly.
Use 2 x 16340 or 2 x 18650 or 2 x 26650;
Positive to laser head;
Never use 3 batteries together;
2. Use a 5V USB wire test the laser head.
Remove the battery tube compartment, there is a interface can connect the 5v USB power.
3. Tight the end cap.