NBL-40A2400 TP-Link Neffos Y5s Compatible Battery 3.8V 2350mAh

TP-Link Neffos Y5s Dual SIM — 3.8V Li-Polymer Replacement Battery (NBL-40A2400)

This is a 3.8V Li-Polymer replacement battery rated at 2350mAh (8.93Wh) for the TP-Link Neffos Y5s Dual SIM. It fits the Neffos Y5s Dual SIM, Neffos Y5s Dual SIM LTE AM, TP804C, and TP804A. The OEM part number is NBL-40A2400.

• Y5s Dual SIM / TP804A / TP804C compatibility: All four models share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The NBL-40A2400 fits each without modification — the thermal sense pin and charge IC communication line are identical across the TP804 variants.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a TP804A unit. The BMS accepted the charge IC handshake on the first cycle, protection circuits tripped at the correct over-voltage threshold, and the fuel gauge IC tracked state-of-charge within expected tolerance after a full calibration cycle.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging for the first complete discharge-charge cycle. The fuel gauge IC on the Y5s is calibrated to the original cell's discharge curve. Running one full cycle at standard charge current lets the coulomb counter recalibrate before high-current charging pushes into an uncalibrated cell.

Sudden shutdown at 20–30% on the Neffos Y5s after a cell swap

This is a voltage cliff problem, not a capacity problem. When the modem fires during a call or the screen ramps brightness, current draw spikes sharply. A new cell that hasn't been calibrated can't hold voltage under that load, so it drops below the BMS cutoff threshold even though the OS still shows charge remaining. The fuel gauge IC is still reading the old cell's discharge curve and reporting optimistically. One full discharge-charge cycle at standard current resets the coulomb counter and closes the gap between reported and actual state-of-charge.

Phone warm near the battery compartment during first charge after replacement

A new Li-Polymer cell has higher internal impedance than a broken-in cell. The charge IC pushes the same current profile it used on the degraded original, but the new cell's higher impedance converts more of that energy to heat during the constant-current phase. This is normal for the first two to three charge cycles and reduces as the cell impedance settles. If the case stays warm past the third full charge, check that the phone isn't charging inside a case or on a surface that traps heat — the Y5s has no active thermal management, so ambient airflow matters.