About this replacement
Apple iPhone 15 — 3.85V Li-Polymer Replacement Battery (A3018)
This is a 3.85V, 3500mAh Li-Polymer replacement battery for the Apple iPhone 15. It fits the iPhone 15 only — not the Plus, Pro, or Pro Max. Voltage and capacity match Apple's OEM specification for this model.
- iPhone 15 fitment: The iPhone 15 uses a specific connector orientation and BMS handshake protocol tied to the A3018 cell. Other iPhone 15 variants run different voltage rails and fuel gauge calibration — this cell is matched to the base iPhone 15 board only.
- Bench tested on actual hardware: We ran this cell through a full charge cycle on an iPhone 15 unit. The BMS accepted the charge handshake without error, and the charge IC stepped through trickle, constant-current, and constant-voltage phases normally.
- Fuel gauge recalibration after install: After fitting this cell, disable fast charging and run one complete discharge-charge cycle at standard 5W. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging pushes current into an uncalibrated coulomb counter.
Sudden shutdown at 20–30% on the replacement cell
A new cell has a discharge curve the iPhone's fuel gauge IC has never seen. Under high-current load — 5G modem switching, ProRAW processing, or screen at full brightness — the cell voltage can dip below the BMS cutoff threshold even when the reported percentage looks safe. The phone reads 25% but the instantaneous voltage under load drops below 3.4V, triggering a hard shutdown. Run one full discharge to 1–2% followed by a complete charge to 100% to let the coulomb counter recalibrate against actual cell capacity.
USB-PD fast charge not accepted on first cycle after replacement
On the first charge cycle, the iPhone 15's charge IC may not negotiate full USB-PD fast charge with a replacement cell — it defaults to a lower current rate while the BMS and fuel gauge IC finish initial calibration. This is not a fault with the adapter or the cell. Use a standard 5W charge for the first full cycle, then reconnect a USB-PD adapter. Fast charge should negotiate normally from the second cycle onward at the expected 18W input rate.