Model YD-10 Light bulb Main light: T6+4*LED Tail light: 5*LED red light Product size/net weight 171G Box size/gross weight Material ABS Switch Press the switch Battery Built-in 2200mAh 18650 battery Charging time/battery life Charging time: 4.5 hours Battery life: 5 hours Charging method Type-C USB charging Gear position Three modes: 4*LED white light - T6 strong light - T6 weak light When the current light is on, the tail light's 5*LED red light flashes in a breathing pattern Zoom mode Fixed focus Waterproof rating IPX4 Lumen/Range 200-300LM 50- 100m Features The backpack with a rear battery compartment features an LED warning light, and the front light can be adjusted up and down by 45 degrees Indicator light 4 LED power indicators: 25%-50%-75%-100% The LED flashes blue when charging The package contains Running light + data cable + leather box packaging 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 to check. If it still doesn't light up, please check the solder joints at the connection between the circuit compartment and the circuit board for any open or loose soldering. If there is any, please re-solder 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 recessed points. Use scissors or a sturdy pair of tweezers to insert into the two recessed points 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 do not resolve the issue, please contact our customer service, and we will assist you in resolving the problem.