Neffos Y5s Dual SIM NBL-40A2400 Replacement Battery 3.8V 2350mAh

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

This is a 3.8V, 2350mAh Li-Polymer replacement battery for the Neffos Y5s Dual SIM. It fits the TP804A and TP804C variants, including the Y5s Dual SIM LTE AM. OEM part number NBL-40A2400 with physical dimensions of 66.84 × 57.80 × 3.60mm.

• TP804A and TP804C compatibility: Both board revisions use the same 3.8V rail, identical connector pitch, and the same charge IC handshake. The NBL-40A2400 cell fits both without any modification to the flex or adhesive seating area.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a TP804C unit. The BMS accepted the charge IC handshake on first connection, held voltage above 3.6V under combined screen and modem load, and tripped protection cleanly below 3.0V.
• Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging and run one full discharge down to auto-shutdown, then charge to 100% uninterrupted. This gives the coulomb counter IC a clean reference curve before fast charge current is introduced to the new cell.

Why the Y5s reports wrong battery percentage after a cell swap

The Y5s uses a coulomb counter-based fuel gauge IC that stores a discharge curve calibrated to the original cell. When a new cell goes in, that stored curve no longer matches the actual voltage-to-capacity relationship of the replacement. The phone reads state-of-charge from the old curve and displays percentages that drift from reality — often showing 40% when the cell is near cutoff. One complete discharge-to-shutdown followed by an uninterrupted full charge resets the IC reference. After that cycle, percentage reporting stabilises.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff event, not a capacity problem. Under peak modem load — during a call handoff or LTE reconnect — instantaneous current demand pulls the cell voltage below the BMS cutoff threshold even though the displayed percentage looks safe. An aged original cell masks this because the fuel gauge has learned to warn earlier. A new cell with an uncalibrated gauge hits the cliff without warning. Run the full discharge-and-recharge calibration cycle described above, and the gauge IC will begin flagging low voltage at the right percentage.