About this replacement
Apple iPhone 11 Pro Max — 3.83V Li-Polymer Replacement Battery (616-00351)
This 3.83V, 3950mAh (15.13Wh) lithium-polymer cell replaces the original battery in the iPhone 11 Pro Max, covering model variants A2161 and A2218. It matches the OEM dimensions at 109.30 × 64.35 × 4.76mm, so it fits the battery bay without modification. Install it when the original cell has lost capacity, shuts down unexpectedly, or no longer holds a charge through a normal day.
- A2161 and A2218 compatibility: Both variants run the same 3.83V power rail, use the same battery connector pinout, and communicate with the same fuel gauge IC — this cell satisfies all three requirements without hardware changes.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on an iPhone 11 Pro Max unit, confirmed BMS handshake, verified the charge IC accepted the cell without fault codes, and checked that the fuel gauge IC began tracking state-of-charge correctly after one complete cycle.
- First-cycle fast charge tip: Disable fast charging for the first complete discharge-charge cycle after installation. The fuel gauge IC needs one full cycle to recalibrate its coulomb counter against the new cell's discharge curve. Running fast charge before that calibration completes can cause the reported percentage to drift by up to 15%.
Why the iPhone 11 Pro Max reports wrong battery percentage after a cell swap
The fuel gauge IC on the 11 Pro Max uses a coulomb counter that was calibrated to the original cell's discharge curve over months of use. When a new cell goes in, that learned curve no longer matches the actual chemistry, so the IC reports a percentage based on stale data. The phone may show 40% and then jump to 60%, or hold at a number and then drop suddenly. One full discharge to automatic shutdown followed by a full charge to 100% forces the IC to rewrite its calibration table against the new cell.
Sudden shutdown at 20–30% on the replacement cell
This happens when the modem or display draws a current spike the cell cannot sustain without its terminal voltage dropping below the BMS cutoff threshold — typically around 3.0V under load on a fresh, uncalibrated cell. The fuel gauge IC hasn't yet mapped where the voltage cliff sits on the new cell, so it doesn't predict the cutoff in advance. The fix is the same recalibration cycle: let the phone discharge fully until it shuts itself off, then charge uninterrupted to 100% without fast charging. After that cycle, the IC knows the new cell's voltage floor and the shutdowns stop.