About this replacement
Fly IQ238 — 3.7V Li-ion Replacement Battery (BL7401)
This is a 3.7V Li-ion cell rated at 1650mAh (6.11Wh), replacing the OEM BL7401 in the Fly IQ238 smartphone. It restores power to a handset that won't hold charge or won't turn on due to a degraded original cell. Voltage and connector match the IQ238 board directly.
- IQ238 platform fit: The BL7401 uses a single-cell 3.7V nominal rail with a three-pin connector carrying the thermistor signal the IQ238's charge IC reads to regulate current. Any cell that doesn't match this pinout causes the device to refuse charging.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on IQ238-class hardware, confirmed the BMS handshake with the charge controller, and verified the thermistor line held within the expected resistance range across the full charge window.
- Fuel gauge recalibration on first install: After fitting this cell, run one full discharge down to automatic shutdown, then charge uninterrupted to 100% before using the phone normally. This lets the IQ238's fuel gauge IC map its coulomb counter to the new cell's actual discharge curve — skipping this step causes percentage jumps and early-shutdown faults.
Why the IQ238 reports wrong battery percentage after a cell swap
The IQ238 uses a fuel gauge IC that stores a learned discharge curve from the original cell. When you install a new cell, that stored curve no longer matches the new cell's actual voltage-to-capacity relationship. The gauge reads voltage and maps it to percentage using old data, so it shows 40% when the cell is nearly flat. One full discharge-to-shutdown followed by a complete uninterrupted charge resets the coulomb counter and rebuilds an accurate curve for the new cell.
Sudden shutdown at 20–30% on the replacement cell
This happens when the modem transmits or the screen backlights at full brightness — both pull a short, sharp current spike the cell must sustain without voltage sagging below the shutdown threshold. A new cell that hasn't completed its first full calibration cycle can hit that threshold earlier than the gauge predicts, triggering an abrupt cutoff while the displayed percentage still looks safe. It is not a faulty cell — it is an uncalibrated gauge. Complete one full discharge-charge cycle, then confirm the phone reaches actual shutdown at or below 3.0V at the battery terminals before concluding there is a cell fault.