About this replacement
Apple iPhone 14 Pro — 3.87V Li-Polymer Replacement Battery (A2866)
This 3.87V, 3200mAh Li-Polymer cell replaces the original A2866 battery inside the iPhone 14 Pro. It fits the 14 Pro only — not the standard 14, 14 Plus, or 14 Pro Max, which each run different cell dimensions and BMS configurations. Capacity is rated at 12.38Wh.
- iPhone 14 Pro fit: The 14 Pro uses a unique cell footprint — 79.30 × 60.10 × 5.20mm — with a dedicated flex connector and BMS handshake tied to Apple's battery health reporting system. This cell matches that physical and electrical spec exactly.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on a 14 Pro unit. The BMS accepted the cell without error flags, and charge current stepped down correctly at each voltage threshold through the CC/CV charging stages.
- Fuel gauge recalibration on first use: After installation, disable fast charging and run one complete discharge-to-charge cycle at standard rate. This lets the fuel gauge IC build an accurate coulomb-count profile against the new cell's discharge curve before high-current charging is introduced.
Why the iPhone 14 Pro reports wrong battery percentage after a cell swap
Apple's fuel gauge IC stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches actual cell chemistry, so the reported percentage drifts from the real state of charge. The IC needs a full discharge and charge cycle to recalibrate its coulomb counter against the replacement cell. Until that cycle completes, the percentage reading can appear several points off in either direction — this is expected behaviour, not a fault in the cell itself.
Sudden shutdown at 20–30% on the replacement cell
This happens when the fuel gauge IC is still running the old cell's discharge curve and misjudges the new cell's voltage cliff. Under heavy load — 5G modem activation or sustained screen brightness — the cell voltage drops faster than the IC predicts, and the phone cuts out before percentage hits zero. One full calibration cycle resolves it in most cases. If shutdowns continue after calibration, check that resting cell voltage holds above 3.80V after a full charge.