[Model] B351 Night Running Light Light bulb 2*T6 (floodlight + spotlight) + 5*LED red light [Product Dimensions] Back: 10.5*5.3*2.7 7*6*3 Net weight 161G [Box size] 13*8*6CM Gross weight 189G [Material] ABS [Switch] Press the switch Battery Built-in 2200mAh 18650 battery [Charging method] micro USB charging [Position] Main light 3 modes: 1*T6 floodlight-1*T6 spotlight strong light-1*T6 spotlight weak light Press and hold the switch to turn on and off. Battery-powered backpack with 5*LED lights, red light breathing flash Zoom Mode Fixed focus Waterproof rating IPX4 Lumen 400-500LM Range 50- 100m Battery life Strong light discharge for about 3 hours [Features] Triangular strap ensures no worries about it falling off during running. The battery compartment on the back of the backpack features an LED warning light The front light can be adjusted up and down by 45 degrees [Indicator light] When charging, the LED indicator on the side of the USB charging port lights up red, and turns green when fully charged [Package includes] Running light + data cable + leather case 1. Check the battery: Make sure the battery has power and insert it into the flashlight in the correct direction. Do not use batteries of different brands, and do not mix old and new batteries. 2. Determine the fault: Unscrew the back part to expose the negative terminal of the battery, then use a metal piece such as a key or tweezers to connect the negative terminal of the battery to the exposed, unoxidized part of the flashlight body, and see if it lights up.If possible, it's a problem with the flashlight switch.Please follow step 3 for inspection. If it still doesn't light up, please check the solder joints between the circuit compartment and the circuit board for any open or loose welds. If there are any, please re-solder them to resolve the issue. 3. Check the tail cover switch: Unscrew the end of the flashlight and you will see that the outer ring of the switch cap has a switch pressure ring with two recesses. Use scissors or a sturdy pair of tweezers to insert into the two recesses and turn clockwise to check if the switch pressure ring is loose. Make sure the switch pressure ring is tightly pressed against the switch and there should be no looseness. 4. Check for poor contact: When the flashlight does not light up or has poor contact, check whether the lamp head is loose, inspect the tail cap to ensure the switch is tightly screwed and well-connected, and ensure that the copper post of the tail cap is in good contact with the metal ring of the tail cap. 5. Other issues: If the above methods still cannot resolve the issue, please contact our customer service, and we will assist you in resolving the problem.