Features: 1.DIY Replaceable Battery Design: Supports 6 removable 18650 batteries (not included), allowing easy battery replacement and extended power life perfect for tech enthusiasts and outdoor users. 2.No Welding Required: Convenient plug-in design makes assembly simple and safe. No soldering tools needed just insert the batteries and start charging instantly. 3.Smart Protection System: Built-in multiple safety protections including overcharge, over-discharge, short circuit, and temperature control to ensure stable operation. 4.High Power Output: Provides stable and efficient power for smartphones, tablets, cameras, and other USB devices suitable for daily use or travel. 5.Durables & Portable Enclosure: Made of high-quality ABS material, lightweight yet sturdy. The compact design fits easily in your bag, making it a great DIY mobile power solution. About old batteries and how to distinguish the positive and negative terminals of batteries: Batteries all have a life cycle. It's not the case that just a few old batteries can be used after being installed. Before purchasing, first make sure that the appearance is intact and the skin is not damaged. The voltage should be between 3.2V and 4.2V. Over time, the internal resistance of a battery will increase. Excessively high internal resistance can affect the normal voltage boost of the motherboard and the current limiting of high-power output loads! !!Our store is not responsible for any malfunctions or other losses caused by installing substandard batteries!! Product Name: Detachable 6-cell Battery Power Bank Kit Color: Black/White Maximum output/input power: 5V-2A Applicable battery: 18650 flat-head battery *6 (battery not included) Dimensions: 137*80*23mm Battery: 115g (casing + mainboard + spring + lens) Note: This product does not include batteries