For iPhone 6 and later, iOS 11.3 and later add new features to show battery health and recommend if you need to replace the battery. You can find these in Settings > Battery > Battery Health (with iOS 16.1 or later, find these in Settings > Battery > Battery Health & Charging).
Battery life. The iPhone 11 Pro Max is powered by the largest battery Apple has put in an iPhone to date - a Li-Ion cell of 3,969 mAh capacity - that's 25% larger than the one inside the XS Max.
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