Features: The 5S 21V Lithiums Battery protections Board features advanced temperature controlled copper hardware and 6MOS 5MOS design, ensuring optimal thermal management and triple layer protections against overcurrent, short circuits, and voltages fluctuations for power tool. Engineered with PCB materials and 3 alloy components, this 5 string protections module maintains structural durability while supporting stable 21V output across demanding industrial applications. for professional technicians, construction workers, and outdoor operators requiring battery safety solution during extended use of cordless drills, and other high drain equipment. for seamless integration with 18650 battery packs in workshops, construction sites, or emergence repair scenarios where continuous power stability and overheating prevention are critical. Its 5S configuration and pre calibrated compatibility with tool systems eliminate installation hassle, delivering maintenancefree operations across temperature variations from 20℃ to 85℃. Specifications: Materials: PCB Size: 8x5.2cm/3.15x2.05inch styles: 6MOS 30, 5MOS 25A(optional) Size: for 21V 5-string battery pack for 18650 batteries Package Includes: 1PC Lithiums Battery protections Board note: Please allow 0-1cm error due to manual measurement. make sure you not mind before bid. Due to the differences between different monitors, the Pictures may not reflect the actual of the item.