About this replacement
Apple iPhone 12 Pro Max — 3.83V Li-Polymer Replacement Battery (A2466)
This 3.83V, 4400mAh lithium-polymer cell replaces the original A2466 battery in the iPhone 12 Pro Max. It fits the A2342, A2410, A2412 regional variants that share the same battery connector and power management interface. Capacity is rated at 16.85Wh, matching the voltage rail the device's PMIC expects.
- iPhone 12 Pro Max platform fit: All iPhone 12 Pro Max regional models route power through the same PMIC and use an identical flex connector pinout. The BMS handshake protocol and charge termination voltage are the same across variants, so one cell covers the full lineup.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on an iPhone 12 Pro Max mainboard. The BMS accepted the cell without a bootloop, charge termination triggered correctly at 4.35V, and the fuel gauge IC began tracking coulombs from the first cycle.
- First-cycle calibration on the 12 Pro Max: On first use after installation, disable fast charging for one complete discharge-charge cycle. The fuel gauge IC is still calibrated to the old cell's discharge curve. Running one slow cycle first lets the coulomb counter recalibrate before USB-PD pushes high current into an uncharacterised cell.
Why the iPhone 12 Pro Max reports wrong battery percentage after a cell swap
The iPhone 12 Pro Max uses a coulomb counter and a learned discharge curve stored by the fuel gauge IC. When you swap the physical cell, that learned curve no longer matches the new cell's actual voltage-to-capacity relationship. The OS reads a state-of-charge estimate that drifts from real capacity, especially in the 20–80% range. One full discharge down to automatic shutdown, followed by a slow charge to 100%, resets the curve and brings percentage readings back in line.
Sudden shutdown at 20–30% on a replacement cell
This happens when the cell voltage drops sharply under load — the modem transmitting or the display at full brightness pulls enough current to cause a voltage cliff. The PMIC interprets that voltage drop as a critically low cell and cuts power to protect the board. It is not a faulty battery. Charge the cell to 100%, run one full uninterrupted discharge, then check whether the shutdowns continue — if the fuel gauge IC has recalibrated, the cliff typically resolves by the second cycle.