Product: T21PD (with light) Key benefits capacity, serviceable battery platform: designed to accept 21 welded 18650 flat cells, giving you a reliable modular power source for devices that use a headtype battery pack. Compact and lightweight for portability: the assembly (case + motherboard + spring basket + lens + lanyard) weighs about 230 g without cells, making it easy to carry, install, or service. Fast power delivery: the T21PD supports PDlevel input/output for efficient charging and device power with multiple voltage/current points to match common devices. What it is and what's included Cell configuration: 21 × 18650 type flat cells (welded), intended for head battery use. Included components: housing/case, motherboard, spring basket, lens, and lanyard. Weight (without cells): approximately 230 grams (case + motherboard + spring basket + lens + lanyard). Physical size: approx. 170 × 84 × 62 mm (about 6.7 × 3.3 × 2.4 inches). Power delivery (T21PD with light): output/input power levels — 5V3A, 9V2A, 12V1.5A. Why customers choose this product Compatibility: Uses standard 18650 flat cells so replacement cells are widely available and easy to service. Spaceefficient design: Compact dimensions and low component weight reduce bulk while preserving functionality. Versatile power routing: PD support at multiple voltages makes it suitable for charging or powering a range of devices that accept 5V/9V/12V PD profiles. Practical assembly: Supplied with the main mechanical and optical parts (case, motherboard, spring basket, lens, lanyard) so you have the core components needed to build or a head battery unit. Performance and reliability Stable mounting and connections enabled by the welded 21cell configuration and spring basket for consistent contact. PD input/output choices help reduce charge time and allow powering devices directly at supported voltages and currents. Durable form factor for repeated handling, installation, and cell replacement. Use scenarios Outdoor lighting/headlamp systems: Build or service a head battery pack for extendedrun flashlight or headlamp setups where portability and replaceable 18650 cells are needed. Portable power solutions: Use as a compact PDcapable battery module to power or charge PDcompatible devices at 5V3A, 9V2A or 12V1.5A during travel, fieldwork, or emergency situations. and refurbishment: Ideal for technicians or hobbyists replacing worn head battery assemblies — includes the main mechanical and optical components to restore functionality. Specifications (concise) Cell type: 18650 flat × 21 (welded) Weight (without cells): ≈ 230 g (case + motherboard + spring basket + lens + lanyard) Dimensions: ≈ 170 × 84 × 62 mm (≈ 6.7 × 3.3 × 2.4 in) Power (T21PD with light): 5V3A, 9V2A, 12V1.5A (output/input) Notes Cells are not included; install quality 18650 flat cells per device requirements and safety guidelines. Use compatible chargers and follow manufacturer recommendations for welding, assembly, and safe handling of battery cells.