The new claim from OnLeaks should be taken with a grain of salt, as the publication noted that the source who provided the rumor is "pretty reliable (not 100% but almost...)."
In comparison, the iPhone 6s features a battery capacity of 1715mAh, while its predecessor, the iPhone 6, was slightly larger at 1810mAh, despite both featuring the same 4.7-inch display. Though larger screens use more power, they also allow for larger batteries, as the 4-inch iPhone 5s series had a battery rated at about 1500mAh.
Apple's so-called "iPhone 7," expected to launch in September, is rumored to be between 6 and 6.5 millimeters thick, making it the thinnest iPhone to date. Despite the smaller frame, however, Apple could fit in a larger battery by shrinking or eliminating some internal components, including the legacy 3.5-millimeter headphone jack.
Apple's new 4.7-inch model is also expected to feature a faster A10 processor, an improved camera (but remaining camera bump), and a base configuration with 32 gigabytes of storage. It's also possible that Apple could bring the True Tone color display, with support for wide color, over from the 9.7-inch iPad Pro.
There hasn't been any indication how big the battery in Apple's anticipated 5.5-inch "iPhone 7 Plus" might be. The iPhone 6s Plus has a battery size of 2750mAh, while the iPhone 6 Plus is rated at 2915mAh.
Beyond a larger screen and bigger battery, the "iPhone 7 Plus" is rumored to feature a dual-lens camera, Smart Connector for magnetic charging, and 3 gigabytes of RAM.