Neffos C9A NBL-40A2920 Compatible Battery 3.85V 2850mAh

Neffos C9A / TP706A — 3.85V Li-Polymer Replacement Battery (NBL-40A2920)

This is a 3.85V, 2850mAh (10.97Wh) Li-Polymer replacement cell for the Neffos C9A and TP706A smartphones. It matches the OEM part number NBL-40A2920 and fits the original battery bay without modification. Voltage, capacity, and connector position match the factory specification.

• C9A and TP706A compatibility: Both models run the same 3.85V power rail, use the same flex connector pinout, and share the NBL-40A2920 footprint. The BMS handshake with the charge IC is identical across both variants, so one cell covers the full range.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the C9A platform and confirmed the BMS communicated correctly with the fuel gauge IC throughout. No false low-battery cutoffs triggered during the test sequence.
• Fuel gauge recalibration after installation: On first use, disable fast charging and run one complete discharge-charge cycle at standard rate. The fuel gauge IC was calibrated to your old cell's discharge curve — letting it map the new cell at low current first prevents early cutoff errors and erratic percentage readings.

Sudden shutdown at 20–30% on the Neffos C9A after a cell swap

This is a voltage cliff issue, not a capacity fault. Under peak load — active LTE radio, screen at full brightness, or a background sync burst — the new cell draws enough current to cause a brief voltage sag. If the fuel gauge IC hasn't completed a full calibration cycle, it reads that sag as a terminal low-voltage event and orders a shutdown even though charge remains. Run one full discharge to around 3.4V under normal use, then charge to 100% without interruption. After that single cycle, the coulomb counter resets its learned curve and the premature shutdowns stop.

Phone won't power on after the replacement battery sat in storage

Li-Polymer cells self-discharge during storage. If this battery shipped or sat unused long enough to drop below roughly 2.5V per cell, the BMS enters a lockout state to prevent damage. The phone will show no response to the power button and may not register on the charger immediately. Connect to a wall charger — not a PC USB port — and leave it for 15–20 minutes without pressing anything. The charge IC will trickle current into the cell until voltage climbs above the BMS recovery threshold, typically 2.8–3.0V, at which point normal charging resumes and the phone will power on.