Like he said, all batteries will have worse performance when cold. But remember every product design has tradeoffs. The iphone (like most all Apple devices) looks is a high priority. The many generations of their products from phones to computers have suffered from other issues due to function being a lower priority. be it batteries in the phones and laptops that have issues, laptop hinges, power adapters, phone antennas, all the way back to the engineering issues with making the PCB in the Apple II look pretty.