Samsung BST2169SE SGH-D400 Replacement Battery 3.7V 850mAh

Samsung SGH-D400 Series — 3.7V Li-ion Replacement Battery (BST2169SE)

This is a 3.7V, 850mAh Li-ion replacement battery carrying OEM part number BST2169SE. It fits the Samsung SGH-D400, SGH-D410, SGH-D415, and SGH-D418 — a family of early-2000s clamshell mobile phones. Voltage and connector match the original spec exactly.

• SGH-D400 family compatibility: The D400, D410, D415, and D418 share the same battery bay dimensions, 3.7V voltage rail, and BST2169SE connector pinout. One cell fits all four without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the D400 platform. The BMS accepted the charge IC handshake on the first cycle, and charge termination triggered correctly at full capacity.
• Fuel gauge recalibration on first use: After installing a new cell, run one full discharge to near-empty before recharging to 100%. The phone's fuel gauge IC was calibrated to the old cell's discharge curve. That single full cycle gives it reference points to report accurate percentages on the new cell.

Sudden shutdown at 20–30% on the SGH-D400 after a cell swap

The D400's fuel gauge IC stores the old cell's internal resistance profile in memory. When a new cell with lower impedance is installed, the IC misjudges how much voltage the cell will sag under the transmit or backlight load. It reads 25% remaining, the cell voltage dips sharply under load, and the protection circuit trips before the OS can react. This produces a hard shutdown with charge still left in the cell. One complete discharge-charge cycle lets the IC rebuild its model against the new cell's actual voltage curve, and the early shutdowns stop.

Phone won't power on after the BST2169SE sat in storage

Li-ion cells self-discharge during storage. If the cell voltage drops below approximately 2.5V per cell, the BMS enters lockout mode to prevent a damaging charge event on an over-discharged cell. Plugging the phone in and seeing no response — no charging animation, no LED — usually means BMS lockout, not a dead cell. Connect the phone to a wall charger and leave it untouched for 15–30 minutes. The charge IC on the phone trickle-charges the cell at low current until voltage climbs above the BMS recovery threshold, typically around 2.9V, at which point normal charging resumes.