Weight is important for a handheld device. 1mm thicker would add a significant chunk of weight. The issue wasn't as much capacity, as it was peak power draw. W

Weight is important for a handheld device. 1mm thicker would add a significant chunk of weight. The issue wasn't as much capacity, as it was peak power draw. While somewhat related to capacity, 10-20% larger battery would not have made much of a difference. They could have crippled the performance and lowering the peak power draw, but that was what they did when it was necessary.