A portable power bank is a compact device designed to store electrical energy, allowing users to charge their electronic devices on the go. These power banks typically come with built-in batteries and various output ports, making them compatible with smartphones, tablets, and other gadgets. They are especially useful during travel, outdoor activities, or emergencies when access to a power outlet is limited. Most portable power banks are rechargeable, meaning they can be powered up using a standard wall charger or USB connection. They vary in capacity, measured in milliampere-hours (mAh), which indicates how much charge they can hold. Higher capacity power banks can charge devices multiple times before needing a recharge themselves.