Convert amperehour to faraday

Battery capacity in milliampere-hours is a charge, not an energy: a 5,000 mAh phone battery can deliver 5 A for an hour, or 500 mA for ten. To compare batteries at different voltages you need watt-hours, energy = charge × voltage: 5,000 mAh at 3.7 V is 18.5 Wh, and a 12 V car battery of 60 Ah holds 720 Wh. Airlines limit power banks by watt-hours (100 Wh without approval, about 27,000 mAh at 3.7 V), which is why the Wh figure is printed on them. One ampere-hour is 3,600 coulombs.

The elementary charge e is the charge of one proton, 1.602 176 634 × 10⁻¹⁹ C, exact by definition since 2019; an electron carries −e. A faraday is the charge of one mole of electrons, 96,485 C, and Faraday's law of electrolysis says it deposits one mole of a monovalent metal: plating 108 g of silver, or 31.8 g of copper, takes one faraday, or 26.8 ampere-hours.