Bea-fon SL810 Replacement Battery 3.7V 1400mAh ICP5/44/61

Bea-fon SL810 / SL820 — 3.7V Li-ion Replacement Battery (ICP5/44/61)

This is a 3.7V, 1400mAh Li-ion replacement battery for the Bea-fon SL810 and SL820 mobile phones. It matches the original ICP5/44/61 cell specification and fits directly into both handsets. Capacity is 5.18Wh, in line with the factory unit.

• SL810 and SL820 shared platform: Both models run on the same mainboard voltage rail with an identical battery bay footprint and connector orientation. The BMS handshake protocol is the same across both, so one cell covers either handset without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the SL810 platform. The BMS accepted the new cell without fault codes, and the charge IC brought it up to 4.2V at the expected termination current.
• Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging if the option is available and run one full discharge-to-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before it begins reporting percentage to the OS — skipping this step causes erratic readings early on.

Why the SL810 reports wrong battery percentage after a cell swap

The SL810 uses a fuel gauge IC that stores a discharge curve calibrated to the original cell. When a new cell goes in, that stored curve no longer matches the actual cell chemistry and impedance. The OS reads percentage from the fuel gauge, not the raw cell voltage, so early cycle readings will be off — sometimes by 15–20%. One complete discharge down to automatic shutoff, followed by a full charge to 4.2V, forces the IC to relearn the curve and corrects the display.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff issue, not a capacity problem. Under modem load — active call, data burst, or screen at full brightness — the cell voltage drops sharply below what the fuel gauge predicted. The phone's protection circuit reads this as an undervoltage event and cuts power before the displayed percentage reaches zero. It happens most often in the first few cycles on a new cell that hasn't been calibrated. Run the phone down to shutdown naturally twice, charging fully between each cycle, and the gauge IC will shift its cutoff threshold to match the actual cell's voltage behaviour.