About this replacement
Apple Watch Ultra 2 — 3.85V Li-Polymer Replacement Battery (A2956)
This 3.85V, 560mAh Li-Polymer cell replaces the original battery in the Apple Watch Ultra 2 (A2686, A2887, 49mm). It restores power to activity tracking, heart rate monitoring, GPS, and notifications. Fit the cell and charge to full before first use — the fuel gauge IC needs a complete cycle after any cell swap.
- Ultra 2 platform fit (A2686 / A2887): Both variants share the same 3.85V rail, connector pinout, and BMS handshake spec, so one cell covers the full Ultra 2 lineup without modification.
- Bench tested on actual hardware: We ran this cell on an Ultra 2 chassis and confirmed the BMS accepted the new cell without a fault flag, voltage held steady through a full charge cycle, and the fuel gauge reported correctly after calibration.
- Post-swap charging requirement: After fitting, place the watch on its magnetic charger immediately and charge to 100% before wearing it. The fuel gauge IC on the Ultra 2 loses its reference point when the cell is disconnected — skipping this step causes the watch to display wildly inaccurate battery percentages for days.
Why the Watch Ultra 2 drains a new cell faster in the first week
A fresh cell has higher internal impedance than a broken-in one. The Ultra 2's always-on display and continuous heart rate sensor pull a steady current, and against a stiffer impedance the BMS reads a steeper voltage drop than the actual state of charge warrants. This makes the watch appear to drain faster than it actually is. After 5–7 full charge cycles the impedance settles, and the fuel gauge recalibrates to match real capacity.
Watch not pairing with iPhone after battery replacement
Removing the battery kills the BLE session entirely — the watch loses its authenticated link to the paired iPhone. This is not a fault with the new cell. Open the Watch app on your iPhone, go to My Watch, tap your watch name, then tap Unpair Apple Watch and re-pair from scratch. The watch reboots into pairing mode at approximately 3.82–3.85V resting voltage once the new cell is seated and charged.