iFixit took apart a North American iPhone 18 Pro and measured the battery at 4,288 mAh. The eSIM iPhone 17 Pro held 4,252 mAh. That is a gain of 36 mAh, about one percent, and in Tom's Guide testing it came with an extra hour of runtime: 16 hours and 17 minutes against 15 hours and 17 minutes last year. Most of that hour belongs to the A20 chip, which is more efficient than the A19 it replaces.
The energy label Apple publishes in Europe puts the iPhone 18 Pro at 4,056 mAh, and European phones still carry a physical SIM tray. The American phone is eSIM only. The space the tray would have taken is worth 232 mAh, or about six percent, and until this teardown nobody outside Apple had the North American figure at all.
Apple's iPhone spec page gives video playback hours and no capacity figure at all, which is why a teardown is the only way to get the number in North America and a regulator is the only way to get it in Europe. Both routes landed within a week of each other this year, and they disagree because they are measuring two different phones.
The iPhone 18 Pro Max's European label reads 5,391 mAh against 4,823 mAh a year ago, an 11 percent jump, while the smaller Pro's moved less than two percent. Anyone choosing between the two sizes on battery is choosing on the bigger phone's cell, not on a lineup-wide upgrade. Replacing either one out of warranty now costs $129, ten dollars more than the iPhone 17 Pro.