Neffos X1 Max Replacement Battery NBL-35A3000 3.85V 2800mAh

Neffos X1 Max — 3.85V Li-Polymer Replacement Battery (NBL-35A3000)

This is a 3.85V 2800mAh Li-Polymer cell replacing the original NBL-35A3000 in the Neffos X1 Max, X1 Max Dual SIM, X1 Max Dual SIM LTE AM, and TP903A. It fits the same footprint at 81.18 × 63.20 × 3.40mm and connects to the same charge IC and fuel gauge circuit. Buy this when your original cell no longer holds charge or the phone shuts down unpredictably.

• X1 Max and TP903A platform fit: The X1 Max, X1 Max Dual SIM, and TP903A all run the same battery bay geometry and share the same BMS connector pinout. One cell covers all variants without any adapter or modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the X1 Max platform. The BMS accepted charge without fault flags, and the protection circuit tripped correctly at the low-voltage cutoff threshold — no runaway, no false stop at mid-capacity.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before the charge IC pushes high current into an uncalibrated cell — otherwise percentage readings stay unreliable for several cycles.

Sudden shutdown at 20–30% on the X1 Max after a cell swap

The X1 Max fuel gauge IC holds a discharge curve learned from the original cell. A new cell with a different internal impedance profile hits a voltage point the IC wasn't expecting, so the phone reads 25% and cuts power the moment the modem or display draws a burst of current. The cell voltage drops below the BMS cutoff threshold under load, even though the resting voltage looks fine. Run one full discharge to below 5% and a full charge to 100% with fast charging off — this recalibrates the coulomb counter against the actual cell curve.

USB-PD fast charge not accepted on the first cycle after replacement

Some proprietary fast-charge protocols on the X1 Max handshake with the charge IC before ramping voltage. On a fresh cell, the BMS may reject that elevated voltage on the first cycle because it has no charge history to verify cell state. Plug in with a standard 5V charger for the first full charge rather than a fast-charge adapter. Once the cell completes one normal cycle, the BMS authorises the fast-charge handshake and the protocol resumes on subsequent charges.