iBaby Q9 Replacement Battery 3.7V 750mAh Li-ion

iBaby Q9 / Q9Ⅱ / Q9M — 3.7V Li-ion Replacement Battery

This is a 3.7V, 750mAh (2.78Wh) Li-ion replacement battery for the iBaby Q9, Q9Ⅱ, and Q9M smartphones. It slots into the original battery compartment and restores the voltage supply the phone needs to run calls, messaging, and background app processes. Use the Capacity figure from this listing — 750mAh — not estimates from third-party sources.

• Q9, Q9Ⅱ, and Q9M fit: All three models share the same 3.7V battery rail, physical footprint (46.20 × 34.14 × 5.68mm), and connector pinout. One cell covers all three variants without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS accepted charge current without tripping, held the voltage rail steady under screen and modem load, and cut off cleanly at the low-voltage threshold.
• Fuel gauge recalibration after swap: On the first use after installation, disable fast charging and run one complete discharge-charge cycle at standard current. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging starts.

Sudden shutdown at 20–30% on the replacement cell

This happens because the fuel gauge IC is still calibrated to the old cell's discharge curve. When the Q9's modem or screen pulls current, the new cell's voltage drops faster than the IC expects, and the phone cuts power before the reported percentage reaches zero. It is not a faulty battery — it is an uncalibrated gauge. Run one full discharge to automatic shutdown, then charge uninterrupted to 100%, and the IC rewrites its reference curve. After that cycle, percentage readings stabilise.

Phone will not power on after the replacement battery sat in storage

Li-ion cells self-discharge in storage. If the cell voltage drops below 2.5V, the BMS locks out to prevent damage and the phone will not respond to the power button at all. Connect the phone to a wall charger — not a PC USB port — and leave it for 15–20 minutes before pressing power. The charge IC needs a brief trickle current phase to bring the cell voltage above the BMS re-enable threshold of approximately 2.9V before normal charging resumes.