Is the last 1% on the iPhone artificially long?
Batteries aren’t like gas tanks where the device just knows how much energy remains. Determining how much energy is in the battery at any given point in time is challenging, and this is exacerbated by the fact that the actual usable energy is affected by momentary external factors such as temperature.
iPhones employ a gas gauge chip that’s responsible for reporting battery percentage. It does this by measuring current as it flows into and out of the battery, and estimating the total amount of energy stored in the battery at any given point in time. The algorithms are quite complex and are generally calibrated to provide a sort of worst-case scenario of how much power is left in the cell.