About this replacement
Samsung SGH-D808 — 3.7V Li-ion Replacement Battery (BST5268BC)
The BST5268BC is a 3.7V, 800mAh Li-ion cell that fits the Samsung SGH-D808 mobile phone. It slots into the original battery bay and connects to the same three-contact terminal the phone uses for charge monitoring and BMS communication. Use this when the original cell no longer holds charge or the phone shuts down without warning.
- SGH-D808 terminal match: The D808 uses a three-pin connector to pass charge data between the battery BMS and the phone's charge IC. This cell uses the same pin layout, so the phone reads cell state correctly rather than throwing a battery error on boot.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on the bench. The BMS held the charge cutoff at 4.2V and tripped the discharge floor before voltage collapsed under load — no forced shutdowns during the test cycle.
- Fuel gauge recalibration on first cycle: On first use after installation, run one complete discharge-to-charge cycle with fast charging disabled. 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 SGH-D808 after a cell swap
The D808's fuel gauge IC stores a discharge curve from the old cell in its coulomb counter. When a new cell goes in, that stored curve no longer matches the actual voltage profile of the replacement. The phone's charge IC interprets a voltage drop under call or screen load as a near-empty cell and forces a shutdown — even when the display shows 25%. One full discharge-charge cycle without interruption resets the coulomb counter to the new cell's curve and stops the premature cutoffs.
Phone feels warm near the battery during the first few charges
A new Li-ion cell has higher internal impedance than a broken-in one. The charge IC on the D808 pushes current at a fixed rate, and the higher resistance of an uncycled cell converts more of that energy to heat during the first few sessions. This is normal for the first two to three charge cycles as impedance drops. If the phone stays warm beyond the third full charge, check that the battery contacts are clean and seated flat — a misaligned terminal increases resistance further and keeps heat elevated.