Compatibility and power source Designed for 21700 batteries (not included). Use only 21700 cells with a flat positive terminal to ensure proper fit and operation. The product relies on standard 21700 form factor so you can choose widely available cells. Important compatibility details Only 21700 batteries with a flat positive electrode are supported. Do not use other battery sizes or nonflat variants, as this can affect fit and safety. Safety and handling Correct polarity is essential. If the battery is inserted with reversed polarity, there is a risk of damage to the motherboard and the protective board, which could lead to a failure or fire. Always verify the direction of the positive and negative terminals before inserting the battery. Design and durability notes The design features a detachable structure for maintenance or battery replacement, but the current construction is not entirely foolproof. Handle assembly and disassembly with care to avoid misalignment or damage. Key benefits Enables use with a common battery format (21700), offering convenient availability and replacement. Clear polarity guidance helps prevent damage to internal electronics. Detachable design supports easy maintenance or battery swaps. Use scenarios Scenario 1: Replacing or upgrading the battery in a device that requires a 21700 flat cell, allowing quick maintenance without special tools. Scenario 2: Integration into a DIY project or modular power setup that uses 21700 cells, enabling flexible battery management. Scenario 3: In a compatible device where regular battery swaps are needed, providing a straightforward replacement path with standard 21700 cells.