Numbers don’t lie.
Apple iPhone 12 (5.4-inch) – A2471 – 2,227mAh
Apple iPhone 12 Max (6.1-inch) – A2431 – 2,775mAh
Apple iPhone 12 Pro (6.1-inch) – A2431 – 2,775mAh
Apple iPhone 12 Pro Max (6.7-inch) – A2466 – 3,687mAh
The A14 chip is rumoured to be a 5nm chip. That would mean a more power efficient chip hence the smaller battery requirement while maintaining the same level of battery life as the current range.