About this replacement
Samsung Galaxy Watch3 45mm — 3.85V Li-Polymer Replacement Battery (EB-BR840ABY)
This 3.85V, 330mAh Li-Polymer cell is a direct cell replacement for the Samsung Galaxy Watch3 45mm. It fits SM-R840 and SM-R845 variants. The OEM part numbers are EB-BR840ABY and GH43-05011A — confirm one of these against your original cell before ordering.
- SM-R840 and SM-R845 compatibility: Both watch variants share the same battery bay dimensions, connector pinout, and BMS handshake profile. The 23.30 × 23.50 × 4.12mm cell fits the chassis without modification, and the flex connector seats on the same ZIF socket on both PCB revisions.
- Bench tested on actual hardware: We ran this cell on SM-R840 units and confirmed the BMS accepted the new cell without throwing a fault code. Charge acceptance was normal from the magnetic cradle, and the fuel gauge IC registered state-of-charge correctly after one full charge cycle post-swap.
- Post-swap charge cycle on the Galaxy Watch3: After fitting the new cell, place the watch on its magnetic charger immediately and run it to 100% before wearing it. The fuel gauge IC on Tizen-based watches loses its calibration reference when the cell is removed — it cannot re-establish accurate state-of-charge tracking without a full charge cycle from near-zero after the swap.
Why the Galaxy Watch3 reports 0% immediately after a battery swap
The Watch3 uses a coulomb-counting fuel gauge IC that tracks charge by measuring current flow over time. When the cell is disconnected, the IC loses its accumulated reference data entirely. On reconnection, it has no baseline, so it defaults to 0% or refuses to display a charge level at all. This is not a fault with the replacement cell. Place the watch on its charger and allow a full uninterrupted charge to 100% — the IC will re-calibrate during that cycle and report accurately from that point forward.
New battery draining to empty in under a day on the Watch3
Always-on display mode combined with continuous heart rate monitoring is the most common cause — these two features together can pull enough current to deplete a 330mAh cell significantly faster than the standard multi-day estimate. Check the watch settings and confirm always-on display is off and heart rate monitoring is set to "every 10 minutes" rather than continuous. If drain persists after adjusting those settings, check whether an active workout is logging in the background — a stuck GPS or workout session holds the sensors at full draw. Disabling always-on display alone typically brings consumption back within the expected range.