The capacity reduction during charging is due to a 30% to 45% energy loss in the battery cells and conversion circuitry. Therefore, a fully charged Anker A1383 Power Bank (PowerCore 20K) offers an estimated 11,000mAh to14000mAh to power devices. To estimate charging cycles, use this formula: (Power Bank Capacity × 0.65) ÷ Device Battery Capacity Number of Charges. For instance, charging a 3,000mAh device using a 20,000mAh power bank would offer approximately 4.33 charges. It depends on the charger's power and the ambient temperature. The A1383 model, when using a 30W PD charger at 77°F (25°C), takes about 4.5 hours to recharge.