About this replacement
Samsung Galaxy Watch Active 2 — 3.85V Li-Polymer Replacement Battery (EB-BR820ABY)
This 3.85V, 320mAh Li-Polymer cell replaces the original EB-BR820ABY battery in the Samsung Galaxy Watch Active 2, including 44mm variants SM-R820 and SM-R825. It restores power to the watch's touchscreen, heart rate sensor, fitness tracking, and notification functions. Dimensions are 24.12 × 23.74 × 5.10mm — measure your original cell before fitting if it has swollen.
- SM-R820 and SM-R825 compatibility: Both the 40mm and 44mm Active 2 variants use the same connector type and BMS handshake protocol. The fuel gauge IC on both boards reads cell impedance on first charge — use the correct capacity cell or the percentage readout will drift.
- Bench tested on actual hardware: We ran this cell on an SM-R825 board. The BMS accepted the new cell without fault codes, the fuel gauge initialised correctly after a full charge cycle, and the heart rate sensor drew current within the normal range for that platform.
- Post-swap charging on Watch Active 2: 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 set an accurate reference point without a full charge cycle starting from near-zero after a cell swap. Skip this step and the percentage display will read inaccurately for days.
Why the Watch Active 2 fuel gauge loses accuracy after a cell swap
The Active 2 uses a coulomb-counting fuel gauge IC that tracks charge in and out of the cell over time. When you disconnect the old cell, the IC loses its stored reference values entirely. It cannot interpolate an accurate state-of-charge from a cold start — it needs to observe a full charge from near-zero to 4.35V to set new upper and lower thresholds. Until that first full cycle completes, readings like "47%" or sudden drops to 1% are normal and not a sign of a faulty replacement cell.
Charge contacts not connecting on the magnetic charger after reassembly
The Active 2 charges via four-pin magnetic pogo contacts on the case back. If the back cover shifts even slightly during reassembly, those contacts can sit 0.5–1mm off-axis from the charger's magnetic array. The charger will still attract magnetically but pass no current. Remove the watch from the charger, inspect the case-back seam for even alignment around the full circumference, press firmly until you feel it seat flush, then place it back on the charger and confirm the charging indicator appears within 10 seconds.