About this replacement
Samsung Galaxy M31 / M31s — 3.85V Li-Polymer Replacement Battery (EB-BM317ABY)
This is a 3.85V, 5850mAh Li-Polymer battery for the Samsung Galaxy M31 and Galaxy M31s smartphones, covering SM-M317F and SM-M317F/DS variants. It replaces OEM part numbers EB-BM317ABY, GH43-05043A, and GH82-23775A. If your original cell is swelling, failing to hold charge, or causing unexpected shutdowns, this is the direct cell swap.
- M31 and M31s share this cell: Both models run the same 3.85V nominal voltage rail, use the same physical connector, and accept the same BMS handshake. The SM-M317F/DS dual-SIM variant draws marginally higher standby current from dual modem activity, but the BMS cutoff thresholds are identical across the range.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on SM-M317F hardware. The BMS accepted the charge IC handshake on the first cycle, protection circuits triggered correctly at low-voltage cutoff, and the cell held stable voltage through a full discharge sweep without sag events.
- Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. The fuel gauge IC in the M31 is calibrated to the old cell's discharge curve. Running one full slow cycle first lets the coulomb counter map the new cell before high-current charging pushes current into an uncalibrated gauge.
Sudden shutdown at 20–30% on the Galaxy M31 after a battery swap
The M31's fuel gauge IC builds its state-of-charge model from the previous cell's impedance and discharge curve. After a cell swap, the stored curve no longer matches the new cell. When the phone hits a voltage point the old curve mapped to 20–30%, the processor load or modem burst causes a voltage dip below the hardware cutoff threshold — and the phone shuts off instantly. This is not a fault with the new cell. Run two full discharge-charge cycles without fast charging. After that, the coulomb counter resets its reference points to the new cell's actual curve, and the percentage readings stabilise.
USB-PD fast charge not activating on the first cycle after replacement
Samsung's Adaptive Fast Charging protocol requires the BMS to signal readiness to the charge IC before high-current delivery begins. On a fresh cell with no charge history, some BMS firmware versions default to a pre-charge trickle phase until cell voltage clears 3.0V per cell. Plugging into a fast charger and seeing slow charge on the first cycle is normal — it is not a defective cell or cable. Once the cell reaches 3.0V and the BMS confirms cell health to the charge IC, the handshake completes and fast charge activates for all subsequent cycles.