This battery box holder fits for 18650 batteries. Simple DIY recharge power supply. You could use this case with your own battery to form power supply system. Item Type: 18650 Battery Holder Box, Material: Plastic + Metal, Color: Black, Fit for: 18650 3.7V battery. Note: Please allow 0-1cm error due to manual measurement and the picture may not reflect the actual color of the item.