TP-Link Neffos X1 Max Replacement Battery NBL-35A3000 3.85V

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

This is a 3.85V, 2800mAh Li-Polymer replacement battery for the TP-Link Neffos X1 Max smartphone. It fits the standard X1 Max, the Dual SIM variant, the Dual SIM LTE AM model, and devices listed as TP903A. OEM part number is NBL-35A3000.

• X1 Max and TP903A compatibility: The X1 Max, Dual SIM, Dual SIM LTE AM, and TP903A all share the same battery bay dimensions, connector pinout, and BMS handshake protocol — one cell covers the entire variant group.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the X1 Max platform. The BMS accepted the cell without fault codes, and the charge IC stepped through trickle, CC, and CV phases correctly.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging and run one full discharge-to-charge cycle before resuming normal use. The fuel gauge IC is still calibrated to the old cell's discharge curve — skipping this step causes the percentage readout to drift until the coulomb counter resets against the new cell's actual curve.

Why the Neffos X1 Max shuts down suddenly at 20–30% after a cell swap

A new Li-Polymer cell has a slightly different voltage-to-capacity curve than the worn cell it replaces. The fuel gauge IC uses a stored model of the old curve to estimate remaining charge. When the new cell's voltage drops faster than the IC expects under modem or display load, the phone hits the hardware low-voltage cutoff before the gauge reaches 0%. The fix is one full uninterrupted discharge cycle — drain to auto-shutdown, then charge to 100% without interruption. After that cycle, the coulomb counter has a real reference point for the new cell and the early shutdowns stop.

USB fast charge not activating on the first cycle after replacement

On the first charge after fitting a new cell, the charge IC may default to standard 5V/1A input and ignore the fast charge handshake. This happens because the IC treats an unrecognised cell state as a precaution — it will not push high current into a cell it has not yet characterised. Plug into a fast charger, let the first full cycle complete at whatever rate the IC allows, and disconnect at 100%. On the second charge cycle, the fast charge protocol re-negotiates normally and full charge current resumes.