important! It is suitable for 21700 flat-head cylindrical lithium batteries, with a length of 70mm and a diameter of 21mm. The battery must be installed from the positive pole, then the negative pole! To disassemble the battery, it must be disassembled from the negative pole, and it is forbidden to disassemble from the positive pole of the battery! Otherwise there is a risk of short circuit! Advantage: The battery holders are made of PC+ABS high quality material. Small size, easy to carry. Easy and convenient to use. Feature: The battery holder has one compartments or chambers for holding one 3.7V battery. It is easy to solder and conduct electricity! Function: Keeping your standard or rechargeable batteries together and safe. Prompts: Batteries Not Included. You had better use consumer type 21700 cell with button cap to get good electricity conductivity of positive and terminal of box. In order to prevent the battery from falling off after installation, the battery box is designed with curved flying wings, so it is difficult to disassemble the battery after it is installed, and plastic auxiliary tools are required, please pay attention. In addition, when using the battery slot, please install the positive pole first, then the negative pole. When removing the battery, remove the negative pole first, then the positive pole. You will get 8 battery slots, which consist of 2 slots 1, 2 slots 2, 2 slots 3, and 2 slots 4. This is a battery slot suitable for 21700 cylindrical lithium batteries. 1, 2, 3, 4 slots, 2 for each, which can be used for PCB layout, electronic DIY, etc. I hope you pay attention , the battery should be removed from the negative pole and installed from the positive pole.