Apple has been steadily pushing iPhone battery capacity upward, and the eSIM version of the iPhone 17 Pro Max is a milestone for the lineup, arriving with a 5,088mAh battery that finally clears the 5,000mAh mark. But a recent battery modification shows that Apple’s previous flagship can technically leap past it—if you’re willing to open the phone and swap parts.
A YouTuber known as DirectorFeng demonstrated a battery upgrade for the iPhone 16 Pro Max that replaces the stock 4,685mAh unit with a larger 5,142mAh cell. That’s not only bigger than the iPhone 17 Pro Max battery on paper, it also represents about a 9.76% increase over the original iPhone 16 Pro Max capacity.
One of the most interesting details from the demonstration is how little the physical characteristics change. According to the video, the upgraded battery adds only a negligible amount of weight, and the dimensions appear close enough that it can fit inside the iPhone 16 Pro Max without needing a redesigned chassis. In other words, this is a capacity bump that doesn’t rely on making the phone thicker or significantly altering internal space—at least in this specific mod.
To verify the battery’s performance, DirectorFeng ran a basic capacity validation process by charging and discharging the new cell three times. The replacement battery module is said to come from SEFU, a company that produces lithium-ion batteries for various products, including iPhones. Third-party iPhone replacement parts like these have been gaining attention, but long-term reliability is still a question mark unless extended testing consistently supports the claims.
After the phone was reassembled, the modified iPhone 16 Pro Max reportedly showed battery health at 100%. However, what wasn’t demonstrated was the real-world endurance comparison people care about most: how this upgraded iPhone 16 Pro Max performs side-by-side against an iPhone 17 Pro Max in sustained use or battery drain testing.
That matters because battery capacity alone doesn’t tell the whole story. Recent battery tests have highlighted how strongly iPhones can perform on efficiency, sometimes matching or beating phones with significantly bigger batteries. An example mentioned alongside the mod is a competing “Pro Max” phone with a massive 7,500mAh battery that still only managed to outlast the iPhone 17 Pro Max by a few minutes—an outcome that underscores how much software optimization and chip efficiency can influence runtime.
For now, the YouTuber says long-term testing is planned for this modified iPhone 16 Pro Max, so clearer answers may come later on retention, stability, and day-to-day gains.
The bigger takeaway is simple: if you have the technical skill to disassemble an iPhone safely and can source compatible parts, a battery upgrade can squeeze more runtime out of an older flagship—potentially even eclipsing newer models in raw mAh. On the other hand, Apple is also rumored to be experimenting with even higher-capacity batteries in future devices, including a foldable iPhone with a battery in the 5,400–5,800mAh range, and a thicker iPhone 18 Pro Max that could make room for a larger cell. If those changes arrive, fewer users may feel tempted to take the DIY route just to get longer battery life.
