About this replacement
Apple Watch SE 44mm — 3.82V Li-Polymer Replacement Battery (A2180)
This is a 3.82V, 290mAh Li-Polymer cell built to the A2180 specification for the Apple Watch SE 44mm. It restores power to the watch's fitness tracking, heart rate monitoring, notifications, and app functions. Swap it when the original cell no longer holds a full day's charge.
- Watch SE 44mm platform fit: The 44mm SE shares the A2180 cell format, voltage rail, and flex connector pinout across its production run. The BMS on this watch validates cell impedance on first charge — using a matched 3.82V Li-Polymer cell prevents a low-voltage fault flag at boot.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the Watch SE 44mm platform. The BMS accepted the cell without fault codes, and the fuel gauge IC initialised correctly after a full charge cycle from near-zero.
- Post-swap charge requirement: After fitting this cell, place the watch on its magnetic charger immediately and charge to 100% before first use. The fuel gauge IC on this platform cannot calibrate its reference point without a complete charge cycle from near-zero following a cell swap — skipping this step causes persistent percentage inaccuracy.
Why the Watch SE 44mm reports 0% immediately after a battery swap
The Watch SE 44mm uses a fuel gauge IC that tracks charge state by coulomb counting from a known reference point. When the cell is disconnected, that reference is lost entirely. The IC reads the new cell's open-circuit voltage, but without a full charge cycle it cannot anchor an accurate state-of-charge calculation. Place the watch on the charger straight after reassembly and let it reach 100% — the gauge resets its reference at full charge, and the percentage display stabilises from that point forward.
Watch not pairing with iPhone after battery replacement
Removing the battery clears the active BLE session between the watch and the paired iPhone. The watch returns from a cold boot without a valid session token, and the iPhone's Watch app cannot reconnect automatically. Open the Watch app on the iPhone, tap your watch under "My Watch," and run through the pairing sequence again — the watch does not need to be erased, just re-paired. Once the BLE handshake completes, all synced data and settings restore from the iPhone backup.