Question: how much does it cost to charge a power bank?
Answer: Far from anything worth being sheepish over, 1 kwh costs about 12 cents. To be specific, your iPhone battery holds a charge of 1,440 mAh, or about 5.45 watt hours. If you fully drained and recharged your phone everyday, then over the course of a year you would have to feed it about 2,000 watt hours, or 2kWh.