About this replacement
Lenovo Vibe S1 Series — 3.85V Li-Polymer Replacement Battery (BL250)
This is a 3.85V, 2400mAh Li-Polymer replacement battery for the Lenovo Vibe S1 smartphone family. It fits the Vibe S1, S1a40, S1a40 Dual SIM TD-LTE, and S1c50. Part number BL250 matches the OEM specification for this lineup.
- Vibe S1 family compatibility: The S1, S1a40, and S1c50 all share the same battery bay geometry, connector pinout, and BMS handshake protocol. BL250 covers the entire series because Lenovo kept a common power architecture across these variants despite differing modem configurations.
- Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on a Vibe S1 unit. The BMS accepted the cell without fault flags, charge termination triggered correctly at 4.35V, and the protection circuit responded normally to load spikes from the dual-SIM modem.
- Fuel gauge recalibration after installation: On first use after fitting this cell, disable fast charging and run one complete discharge-to-charge cycle. This allows the fuel gauge IC to map its coulomb counter against the new cell's discharge curve before high-current charging begins on an uncalibrated reference.
Sudden shutdown at 20–30% on the Vibe S1 after a cell swap
This happens when the fuel gauge IC is still referencing the old cell's voltage-to-capacity curve. The new cell hits a voltage cliff under modem or display load at a point the gauge still reads as 25% — and the phone cuts power before the OS can log a low-battery event. The fix is a full uninterrupted discharge to automatic shutdown, followed by a full charge to 100% with fast charging off. After one complete cycle, the coulomb counter recalibrates and the shutdowns stop.
Percentage jumping erratically in the first two days after replacement
The fuel gauge IC on the Vibe S1 uses a stored discharge profile to estimate state of charge. When a new cell goes in, that profile no longer matches the actual cell chemistry, so the reported percentage can jump 5–15% in either direction between readings. This is not a fault with the cell — it is the IC recalibrating. Run two full discharge-charge cycles without interruption and the readings will stabilise. If erratic reporting continues past three full cycles, check that the battery connector is fully seated and making clean contact on all four pins.