DIY rechargeable 9V square battery:
This requires some hands-on ability, including materials and tools such as PVC board, strong adhesive, scrapped 9V square batteries, TP4056 ternary lithium battery charging module, etc.
Cut the PVC board according to a certain size and bond it together. After polishing it flat, fix the battery buckle and connect the wires.
Install the charging module and polymer lithium battery, adjust the boost module to around 9V, and you can start charging.
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