Samsung SPH-A400 BEX070DSE Replacement Battery 3.7V 1000mAh

Samsung SPH-A400 Series — 3.7V Li-ion Replacement Battery (BEX070DSE)

The BEX070DSE is a 3.7V Li-ion cell rated at 1000mAh (3.7Wh), built to fit the Samsung SPH-A400, SPH-A405, and SPH-A250 flip phones. These early 2000s Samsung handsets share an identical battery bay, connector pin-out, and BMS handshake protocol, so all three models draw from the same cell specification. This listing covers all three.

• SPH-A400, A405, and A250 compatibility: All three models use the same physical form factor, matching contact orientation, and identical voltage rail at 3.7V nominal. The BMS in each handset communicates over the same two-wire protocol, so the cell swap is direct with no adapter or firmware change needed.
• Bench tested on actual hardware: We ran this cell through a full charge cycle and verified the BMS accepted the charge handshake without fault flags. Charge current ramped normally from constant-current into constant-voltage phase, and the protection circuit tripped correctly at low-voltage cutoff during discharge.
• Fuel gauge recalibration after installation: On first use after fitting, run one complete discharge down to automatic shutdown, then charge uninterrupted to 100% before using the phone. This lets the fuel gauge IC map the new cell's discharge curve. Skipping this step can leave the coulomb counter reading against the old cell's worn profile, causing percentage jumps or early shutdowns.

Why the SPH-A400 shuts down suddenly at 20–30% after a cell swap

The SPH-A400's fuel gauge IC stores a discharge curve from the previous cell. When a new cell with higher internal resistance than the worn original is installed, the IC underestimates how much voltage the cell will sag under load from the RF transmitter or backlight. At around 3.6–3.65V, the load spike pulls the cell below the BMS cutoff threshold even though the displayed percentage still reads 20–30%. The fix is one full supervised discharge-to-shutdown cycle followed by a full uninterrupted charge. After that single cycle, the IC recalibrates its voltage-to-capacity mapping against the new cell's actual curve.

Phone shows incorrect battery percentage after fitting the BEX070DSE

The coulomb counter in these Samsung models does not auto-reset when the cell is swapped. It carries over accumulated error from the degraded original battery, so percentages can read high or jump erratically in the first few cycles. A single full discharge — letting the phone reach automatic shutdown — followed by a complete charge cycle forces the fuel gauge IC to re-anchor its zero and full-charge reference points. After that calibration cycle, percentage reporting stabilises. If jumps persist past three full cycles, check that the battery contacts in the bay are clean and making firm contact.