Neffos X1 Compatible Battery NBL-38A2250 3.85V 2150mAh

Neffos X1 / TP902C — 3.85V Li-Polymer Replacement Battery (NBL-38A2250)

This is a 3.85V, 2150mAh (8.28Wh) Li-Polymer cell that replaces the original NBL-38A2250 in the Neffos X1, X1 Dual SIM, and TP902C smartphones. It restores full electrical capacity to the mainboard, display, modem, and application processor. Physical dimensions are 64.00 × 56.20 × 3.40mm — confirm these against your existing cell before fitting.

• X1, X1 Dual SIM, and TP902C compatibility: All three share the same chassis footprint, connector pinout, and BMS handshake protocol, which is why a single cell covers the full range. The Dual SIM variant draws slightly higher standby current on the second modem, but the voltage rail and BMS communication remain identical.
• Bench tested on actual hardware: We cycled this cell through a full discharge-charge sequence on the TP902C. The BMS accepted the charge IC handshake on the first cycle, voltage held steady under simultaneous screen and LTE load, and no cutoff events were triggered during the test.
• Fuel gauge recalibration on first cycle: After fitting, disable fast charging and run one complete discharge-charge cycle at standard current. The fuel gauge IC is still calibrated to the old cell's discharge curve — one slow cycle lets it remap against the new cell before high-current charging begins.

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

This happens when the fuel gauge IC's stored discharge curve no longer matches the new cell's actual voltage-versus-capacity profile. The phone's SoC calculates remaining charge from a coulomb counter calibrated to the old cell. When the new cell's open-circuit voltage drops faster than the model predicts — typically around 3.65–3.70V under modem or display load — the protection circuit interprets it as a hard undervoltage event and shuts down immediately. Running one full discharge to ~3.0V and a complete charge cycle forces the fuel gauge IC to resample the new curve. After that cycle, the reported percentage tracks the actual cell state correctly.

Phone warm near the battery area on the first few charges after replacement

A new Li-Polymer cell has slightly higher internal impedance than a cell that has completed its initial formation cycles. The charge IC compensates by pushing a higher voltage differential across that impedance, which produces more heat than normal during the first two or three charge sessions. This is not a fault — it resolves as the cell completes formation cycling. If the phone feels hot to the touch rather than warm, stop the charge, let it cool to room temperature, and check that the connector is fully seated before resuming.