Bea-fon SL650 Replacement Battery 3.7V 800mAh Li-ion

Bea-fon SL650 — 3.7V Li-ion Replacement Battery (SL650)

This is a 3.7V, 800mAh Li-ion battery for the Bea-fon SL650 mobile phone. It fits the SL650 directly and restores full device operation when the original cell has degraded or failed. Capacity is rated at 2.96Wh, matching the stock specification.

• SL650 platform fit: The SL650 uses a slim, low-draw phone architecture with a fixed connector layout. This cell matches the voltage rail and physical footprint that the SL650 charging IC and BMS expect — no adapter or modification needed.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on the SL650 platform. The BMS accepted the cell without fault flags, and the charge IC reached full termination voltage cleanly.
• Fuel gauge recalibration on first use: On first use after installation, run one complete discharge-charge cycle before relying on the battery percentage indicator. This lets the fuel gauge IC map the new cell's discharge curve accurately. Skipping this step often causes percentage jumps or early shutdown warnings.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff problem, not a capacity problem. When the SL650 powers the modem or screen at peak draw, a new uncalibrated cell can drop below the BMS cutoff voltage momentarily — even when the reported percentage looks healthy. The phone shuts down to protect the cell, not because it's empty. One full discharge-charge cycle recalibrates the coulomb counter and moves the cutoff trigger to the correct state-of-charge point.

Phone warm near the battery during the first charge cycle

A new Li-ion cell typically has higher internal impedance on its first cycle. The SL650 charge IC pushes current into that higher resistance, and some of that energy converts to heat rather than stored charge. This is normal and reduces after the first full cycle as the cell's internal impedance settles. If the phone feels hot to the touch — above what you'd expect from normal use — remove it from charge and let it cool to room temperature before continuing.