Before the USB Power Delivery 2.0 spec became reality, battery packs maxed out at a charge of about 15 Watts (5 volts at 3 amps). PD 2.0 increased the max to 100W, but most of the batteries implementing PD 2.0 strike a balance of performance, heat, cost, and compactness by outputting about 30W. Some recharge at the same rate while others are much slower.
However, the PD 2.0-based ZMI PowerPack 20000 ($80) offers 40 watts of power over USB-C to charge laptops while they’re in active use. And the 72 watt-hour/20,000 milliampere-hour PowerPack 20000 recharges itself at 45W. It’s faster in both directions than nearly every USB-C battery pack on the market.