Bird S1150 Replacement Battery 3.7V 850mAh Li-ion

Bird S1150 — 3.7V Li-ion Replacement Battery

This is a 3.7V Li-ion cell rated at 850mAh (3.15Wh), built to replace the original battery in the Bird S1150 mobile phone. It fits the S1150 directly — no modification required. Use this when the original cell no longer holds a charge, swells, or fails to power the device on.

• S1150 platform fit: The S1150 runs on a single-cell 3.7V Li-ion architecture with a low-current BMS sized for entry-level smartphone loads — calls, messaging, and basic apps. This cell matches that voltage rail and connector geometry.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a controlled rig, checking BMS handshake, cutoff voltages, and thermal behaviour at full charge current. The cell accepted charge without lockout and discharged cleanly to the BMS low-voltage cutoff.
• Fuel gauge recalibration after swap: On first use after installing this cell, run one full discharge down to auto-shutoff, then charge to 100% without interruption. This gives the S1150's fuel gauge IC a clean reference curve for the new cell before normal use.

Why the S1150 shows wrong battery percentage after a cell swap

The S1150 uses a fuel gauge IC that learns the discharge curve of the installed cell over time. When you swap in a new cell, the IC still references the old curve it built for the degraded original. The percentage reading drifts — sometimes showing 40% when the phone is about to shut down, or 20% when the cell still has capacity. One full uninterrupted discharge-charge cycle resets the coulomb counter and re-anchors the gauge to the new cell's actual curve.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff, not a capacity fault. Under load — modem transmitting, screen on full brightness — the cell voltage drops sharply below the threshold the OS uses to estimate remaining charge. The fuel gauge reads 25% but the actual cell voltage under load has already hit the BMS cutoff, so the phone shuts off. It typically recovers fully on recharge. Running one complete calibration cycle after installation reduces how often the gauge misreads the cliff point.