About this replacement
Apple Watch Ultra A285 / A2622 / A2684 — 3.86V Li-Polymer Replacement Battery (A2749)
This 3.86V, 540mAh Li-Polymer cell replaces the original A2749 battery inside the Apple Watch Ultra and the A285, A2622, and A2684 variants. It fits the smartwatch chassis directly and restores power to the display, processor, heart rate sensor, and wireless radios. Voltage and physical dimensions match the OEM cell: 33.00 × 30.70 × 5.20mm.
- Ultra and associated watch variants: The A285, A2622, A2684, and Watch Ultra share the A2749 cell specification — same voltage rail, same connector pinout, and the same BMS handshake protocol. One cell covers the full group.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the Watch Ultra platform. The BMS accepted the new cell without fault codes, fuel gauge re-initialised on first full charge, and the health indicator reported correctly in watchOS settings.
- Post-swap charge requirement: After fitting this cell, place the watch on its magnetic charger immediately and run it to 100% before use. The fuel gauge IC on this platform loses its charge reference when the cell is removed. Without that first full cycle, the percentage readout will be inaccurate and the watch may shut off without warning.
Why the Watch Ultra drains the A2749 cell faster than older Apple Watch models
The Ultra runs a larger always-on display, an L1 GPS chip, and a continuous heart rate sensor simultaneously — a current profile significantly heavier than the Series 4 or SE. The A2749 cell at 540mAh is the OEM-specified capacity for this load, not an undersized afterthought. If drain feels excessive in the first week after a swap, the fuel gauge IC is still recalibrating its discharge curve against the new cell's impedance. Run two full charge-discharge cycles before drawing conclusions about capacity.
Watch shows 0% and won't turn on immediately after battery swap
This is a fuel gauge IC issue, not a faulty cell. When the original battery is disconnected, the MAX1726x-series fuel gauge on this platform loses its learned reference voltage and defaults to 0% or refuses to boot. The fix is straightforward: connect the watch to its magnetic charger without pressing any buttons and leave it for at least 30 minutes before attempting to power on. Once the cell reaches approximately 3.7V, the watch will boot and the gauge will begin recalibrating normally.