About this replacement
Samsung Galaxy S24 FE / SM-S721 — 3.88V Li-Polymer Replacement Battery (EB-BS721ABY)
This is a 3.88V, 4500mAh Li-Polymer replacement battery for the Samsung Galaxy S24 FE (SM-S721, SCG30, SM-S7210). It replaces OEM part EB-BS721ABY and fits the same connector and form factor as the original cell. Capacity is rated at 17.46Wh, matching the stock specification.
- S24 FE platform fit: The SM-S721 series shares a common battery bay geometry, flex connector pinout, and BMS handshake protocol across regional variants including SCG30 and SM-S7210. All these models pull from the same EB-BS721ABY cell specification, so one replacement covers the full variant range.
- Bench tested on actual hardware: We ran this cell on an SM-S721 unit and confirmed the BMS initialised correctly on first boot — charge accepted via both standard and fast-charge protocols after the fuel gauge IC completed its first calibration cycle.
- Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current fast charging pushes significant current into an uncalibrated cell.
Why the S24 FE reports wrong battery percentage after a cell swap
The S24 FE uses a coulomb counter tied to a fuel gauge IC that was calibrated against the original cell's discharge curve over hundreds of cycles. When you swap in a new cell, that stored curve no longer matches the physical cell. The IC initially reports percentage based on stale data, which is why you may see jumps or sudden drops. One full discharge-to-charge cycle — from above 90% down to automatic shutdown and back to 100% — forces the IC to rewrite its reference curve to the new cell.
Sudden shutdown at 20–30% after replacement
This is a voltage-cliff failure, not a capacity problem. Under heavy load — 5G modem transmit, high-brightness display, or background processing — the cell voltage drops sharply below the BMS cutoff threshold before the fuel gauge reports 0%. The phone shuts down because actual cell voltage has fallen below approximately 3.4V even though the percentage readout hasn't caught up. Run the full fuel gauge recalibration cycle described above first. If shutdowns persist after two full cycles, check that the flex connector is fully seated — a partial connection increases internal resistance and amplifies voltage sag under load.