About this replacement
Samsung Galaxy S25 5G — 3.9V Li-Polymer Replacement Battery (EB-BS931ABY)
This is a 3850mAh Li-Polymer replacement battery for the Samsung Galaxy S25 5G. It fits SM-S9310, SM-S931B, SM-S931B/DS, and related variants. Voltage is 3.9V nominal, matching the original cell specification.
- SM-S931 series compatibility: Every SM-S931 variant shares the same 68.60 × 62.20 × 4.60mm cell footprint, connector pinout, and BMS communication protocol. The fuel gauge IC reads charge state over the same data line across all regional builds — DS (dual-SIM) and single-SIM boards included.
- Bench tested on actual hardware: We ran this cell on an SM-S931B board and confirmed BMS handshake, charge acceptance from 0% to 100%, and correct voltage reporting at 4.35V full-charge cutoff. The charge IC accepted standard and fast-charge current profiles without fault flags.
- Fuel gauge recalibration on first use: After installation, disable fast charging in Settings and run one complete discharge-charge cycle at standard current. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging begins on an uncalibrated cell.
Sudden shutdown at 20–30% on the replacement cell
This is a voltage cliff, not a capacity fault. Under peak modem load or display brightness, a fresh cell with an uncalibrated fuel gauge IC can sag below the board's minimum voltage threshold before the percentage reaches zero. The phone shuts down to protect the SoC even though the reported percentage looks safe. One full discharge-to-shutdown followed by a complete charge cycle lets the coulomb counter anchor to the real cell curve and eliminates most premature cutoffs.
USB-PD fast charge not accepted on first cycle after swap
On the first charge after a cell replacement, the charge IC sometimes defaults to trickle current while it verifies BMS authentication. This is normal — the charger negotiates voltage and current with the BMS, and until the BMS confirms cell state, it limits input. Plug into a USB-PD charger, wait five minutes, then unplug and reconnect. If fast charging still does not engage after a full standard-current charge cycle, check that the battery connector is fully seated — a partial connection raises contact resistance and the charge IC interprets this as a fault.