Power Bank
Also known as: portable charger, mobile battery, USB power bank
A portable battery in a pocket-sized case that charges phones, tablets, and small USB devices when no wall power is available.
A power bank is a rechargeable lithium battery in a protective case, with one or more USB output ports for charging phones, tablets, headphones, smartwatches, and similar small devices. You charge the power bank from a wall socket when convenient and use it as a portable energy source when away from outlets — travel, commuting, outdoor activities, or during a power outage.
Capacity is rated in milliamp-hours (mAh). A 10,000 mAh power bank typically delivers about 2 full smartphone charges (real-world delivered capacity is usually 60-70% of the rated figure due to voltage conversion losses). For everyday carry, 10,000-20,000 mAh is the sweet spot. For multi-day travel or as part of an emergency kit, 20,000-30,000 mAh is more useful.
Output matters as much as capacity. Look for power banks with USB-C Power Delivery (PD) and at least 18W output if you want to fast-charge a modern phone. Pass-through charging (charging the bank while it charges a device) is convenient. Airlines limit lithium batteries to 100Wh in carry-on baggage — most consumer power banks are well under this limit, but check before flying with larger units.