Bird SC04 Replacement Battery 3.7V 900mAh Li-ion

Bird SC04 — 3.7V Li-ion Replacement Battery

This is a 3.7V Li-ion cell rated at 900mAh (3.33Wh), built to replace the original power cell in the Bird SC04 smartphone. It fits directly into the SC04 and restores basic phone functions — calls, messaging, and apps — when the original cell has degraded or failed. Voltage and capacity match the factory specification for this handset.

• SC04 platform fit: The Bird SC04 uses a low-voltage 3.7V single-cell Li-ion configuration with a compact 900mAh capacity. The charge IC and fuel gauge IC on the SC04 mainboard are calibrated to this voltage window. Swapping to a cell outside that specification causes charge termination errors or inaccurate percentage readings.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge sequences, confirmed BMS cutoff triggers at the correct low-voltage threshold, and verified that the charge IC accepted the cell without fault flags on the first cycle.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-to-charge cycle. The SC04 fuel gauge IC reads a stored discharge curve from the old cell — letting it run one full unassisted cycle against the new cell teaches it the actual voltage curve before high-current charging is applied.

Sudden shutdown at 20–30% on the replacement cell

The Bird SC04 fuel gauge IC holds a discharge curve model built from the old cell's behaviour. When you install a new cell, that model is stale — the IC predicts voltage based on data that no longer matches. Under load from the modem or display, the new cell's actual voltage drops below what the IC expects at that percentage, triggering an emergency shutdown. Run one full discharge from 100% down to automatic shutdown, then charge uninterrupted to 100% without unplugging early. After that cycle, the fuel gauge recalibrates its model against the new cell and the premature cutoff stops.

SC04 not powering on after the replacement cell sat in storage

Li-ion cells self-discharge in storage. If a replacement cell has been stored for several months before installation, its resting voltage may have dropped below 2.5V — the threshold where the BMS engages a lockout to prevent damage. The SC04 will show nothing when you press the power button, and a standard charger plug may not wake it. Connect the phone to a charger and leave it for 15–20 minutes without pressing anything; most BMS circuits accept a trickle current at this stage and will release the lockout once the cell climbs back above 2.8V, after which the phone boots normally.