About this replacement
Samsung Galaxy S21+ — 3.86V Li-Polymer Replacement Battery (EB-BG996ABY)
This is a 4700mAh Li-Polymer replacement battery for the Samsung Galaxy S21+ and Galaxy S21+ 5G. It fits SM-G996W, SM-G9960, and related SM-G996 variants. Voltage is 3.86V, matching the original cell specification.
- SM-G996 variant compatibility: All SM-G996 models share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The EB-BG996ABY part number covers the full S21+ lineup — regional variants differ only in radio bands, not power architecture.
- Bench tested on actual hardware: We ran this cell in an SM-G996W unit and confirmed the BMS accepted the charge IC handshake without error flags. The coulomb counter initialised correctly on the first full discharge cycle with no voltage cutoff anomalies.
- Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve before high-current fast charging pushes current into an uncalibrated state.
USB-PD fast charge not working on the first cycle after replacement
After a cell swap, the S21+ charge IC sometimes refuses to negotiate USB-PD or the Samsung Adaptive Fast Charging protocol on the first cycle. The BMS on a fresh cell starts with a conservative charge profile until it completes one full handshake sequence with the phone's PMIC. This is not a fault — it is the cell's protection circuit running a first-cycle verification pass. Charge the phone once at standard 5W to completion, then fast charging will engage normally on subsequent cycles.
Sudden shutdown at 20–30% after fitting a replacement cell
This happens when the fuel gauge IC is still calibrated to the old cell's voltage-to-capacity curve. The S21+ modem and display draw sharp current spikes, and if the gauge reports 25% but the actual cell voltage drops below the cutoff threshold under that load, the phone shuts off immediately. The fix is a full discharge to auto-shutdown followed by an uninterrupted charge to 100% — this resets the coulomb counter against the new cell's actual capacity. After one complete cycle, the percentage readout stabilises and the shutdowns stop.