About this replacement
Samsung X620 / X628 — 3.7V Li-ion Replacement Battery
This is a 3.7V, 700mAh (2.59Wh) lithium-ion cell for the Samsung X620 and X628 mobile phones. It replaces the original battery when the existing cell no longer holds charge or causes unexpected shutdowns. Dimensions are 69.71 × 42.46 × 5.82mm — check these against your original before installing.
- X620 and X628 compatibility: Both models share the same battery bay dimensions, connector pinout, and BMS handshake protocol, so a single cell fits either device without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the X620 platform. The BMS accepted the charge IC handshake on the first cycle, and the protection circuit tripped correctly at the rated low-voltage cutoff under load.
- Fuel gauge recalibration after install: On first use after fitting, disable any fast-charge feature and run one complete discharge-to-charge cycle. This allows the fuel gauge IC to map the new cell's discharge curve before high-current charging begins on an uncalibrated cell.
Sudden shutdown at 20–30% on the Samsung X620
This is a voltage cliff issue. Aged or newly swapped Li-ion cells can drop below the modem and display's minimum sustain voltage while the OS still reports 20–30% remaining. The phone cuts out because the cell cannot deliver the instantaneous current the radio or screen demands, even though the coulomb counter hasn't reached zero. The fix is one full calibration cycle — drain to auto-shutoff, charge uninterrupted to 100%. After that cycle, the fuel gauge IC aligns its model to the actual cell curve.
OS reporting wrong battery percentage after a cell swap
The X620's fuel gauge IC stores a discharge curve calibrated to the original cell. Swapping in a new cell doesn't reset that stored model automatically. The result is percentage readings that jump, stall, or drop sharply near the end of a charge. Run the phone from full charge down to auto-shutoff, then charge to 100% in one uninterrupted session — this forces the IC to rewrite its reference curve against the new cell's actual behaviour. After one full cycle, percentage reporting stabilises.