Features: Widely compatibility design, the 21700 battery box can connection in series and parallel, suitable for various battery configurations. Through flexible series and parallel connection, users can freely combine batteries according to their needs to meet different requirements. The unique design makes battery replacement simple and efficient, reducing the complex step of traditional battery holder installation. Using high-strength plastic material to ensure long time use without easy damage. Suitable for circuit boards, electric toys, digital photo frame, electronic calendars, and other digital products. For storage convenience, the battery box on the device serves as a battery holder. Specifications: Material: plastic Parameters: Suitable for 21700 lithium batteries, supports series and parallel connection Size: Standard battery tank design Type: Single section installation / 2 section installation / 3 section installation Length: approx. 82.7mm/3.25inch Practicality: Widely used in DIY electronic projects, mobile power assembly and other occasions where flexible battery configuration is required Package Includes: 1 Piece 21700 Battery Box note: Please allow 1-2cm errors due to manual measurement. Please allow for slight color differences due to different display resolution.