Neffos C5 Plus Replacement Battery NBL-40A2150 3.8V 2050mAh

Neffos C5 Plus / TP7031A / TP7031C — 3.8V Li-ion Replacement Battery (NBL-40A2150)

This is a 3.8V, 2050mAh (7.79Wh) Li-ion cell for the Neffos C5 Plus smartphone, covering model variants TP7031A and TP7031C. It replaces OEM part numbers NBL-40A2150 and NBL-40B2150. Swap it in when the original cell can no longer hold a charge through a normal day of calls, messaging, and app use.

• C5 Plus variant coverage (TP7031A / TP7031C): Both sub-variants share the same 3.8V voltage rail, connector pinout, and BMS handshake protocol — one cell covers both. The NBL-40B2150 suffix is a minor revision, not a separate spec.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the C5 Plus platform. The BMS accepted the handshake cleanly, charge current stepped down correctly at CV phase, and there were no spurious low-voltage cutoffs during moderate load.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging begins on an uncalibrated reference.

Sudden shutdown at 20–30% on the C5 Plus after a cell swap

This is a voltage cliff issue, not a capacity defect. Under peak load — modem transmit bursts or screen-on with background sync — the new cell's internal resistance causes a momentary voltage drop the protection circuit reads as undervoltage. The phone shuts down even though the coulomb counter says 20–30% remains. One full discharge-charge cycle lets the fuel gauge IC recalibrate the empty-threshold mapping to the new cell, which typically stops the early shutdowns. After calibration, the cutoff should align with an actual resting voltage of around 3.4–3.5V per cell.

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

Li-ion cells self-discharge in storage, and if the cell dropped below approximately 2.5V, the BMS enters lockout mode to prevent damage — the phone will not respond to the power button. Connect the phone to a wall charger rated at least 5V/1A and leave it for 15–20 minutes without pressing anything. The BMS needs a trickle current to recover cell voltage above the lockout threshold before it will allow normal boot. If the charge LED does not appear within 30 minutes, try a different cable — some USB cables lack sufficient wire gauge to deliver the trickle current the BMS needs to exit lockout.