About this replacement
Bea-fon SL550 — 3.7V Li-ion Replacement Battery (SL550)
This 3.7V 1100mAh Li-ion battery replaces the original cell in the Bea-fon SL550 mobile phone. It fits the SL550 directly, matching the OEM voltage and physical dimensions of 46.00 × 40.10 × 6.30mm. Use it when the original cell no longer holds a charge or the phone fails to power on.
- SL550 platform fit: The SL550 uses a fixed 3.7V single-cell Li-ion architecture with a proprietary connector and BMS handshake tied to the original cell's internal resistance profile. This replacement matches that voltage rail and connector pinout so the phone's charge IC accepts it without triggering a protection fault.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the SL550 platform. The BMS accepted the cell without cutoff errors, and the protection circuit held within spec across the full charge window from 3.0V to 4.2V.
- Fuel gauge recalibration on first use: On first use after installation, run one complete discharge-to-charge cycle before enabling any fast-charge mode. This gives the fuel gauge IC time to map the new cell's discharge curve — skipping this step causes the percentage counter to read against the old cell's calibration data.
Why the SL550 reports wrong battery percentage after a cell swap
The SL550's fuel gauge IC stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches the actual voltage-to-capacity relationship of the replacement. The gauge reads voltage, maps it against the old curve, and outputs a percentage that can be off by 15–25%. One full discharge below 3.2V followed by a full charge to 4.2V forces the IC to rewrite its calibration against the new cell.
Sudden shutdown at 20–30% remaining on the SL550
This happens when the cell voltage drops sharply under load — typically during a call or screen-on burst — faster than the fuel gauge predicted. The phone shuts down not because capacity is gone, but because voltage sags below the BMS cutoff threshold under that momentary current draw. It is more common in the first few cycles before the gauge recalibrates. Run two full discharge-charge cycles and check that resting voltage after a full charge reads at or above 4.15V.