A:Answer To get a rough estimate, you can use the following formula:
(Number of recharges) = (Power bank capacity in mAh) * (Efficiency) / (Phone battery capacity in mAh)
For example, if you have a phone with a 3000mAh battery and we assume an efficiency of 80%, the calculation would be:
(Number of recharges) = (20000mAh) * (0.8) / (3000mAh)
(Number of recharges) = 16000mAh / 3000mAh
(Number of recharges) ≈ 5.33