KAKUSIGA 10000mAh 22.5W Fast-Charging Power Bank

Five dollars for ten thousand milliamp-hours with real fast charging behind it. At up to 22.5 W with Power Delivery support, this refills a compatible phone at close to wall-socket speed rather than the slow trickle a cheap pack usually manages.

Two outputs, a USB-C and a USB, so a phone and a pair of earbuds can charge at once — which is most of what a spare battery gets asked to do on a day out. Compact enough for a bag rather than a pocket. One month of warranty at this price.