Byone M15X Laptop Compatible Battery 14.8V 4000mAh

Byone Alienware M15X / M15RX — 14.8V Li-Polymer Replacement Battery (36539419s)

This is a 14.8V, 4000mAh (59.2Wh) Li-Polymer replacement battery for the Alienware M15X and M15RX gaming laptops. It uses OEM part number 36539419s and connects directly to the original battery bay without modification. Voltage and capacity match Dell's original specification for these two models.

• M15X and M15RX platform fitment: Both models share the same 14.8V four-cell battery architecture, identical connector pinout, and the same BMS handshake protocol with the Alienware EC firmware. One cell fits both.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the M15X platform. The BMS communicated correctly with the EC, charge current ramped as expected, and the cell hit rated capacity at cutoff.
• First-cycle discharge reset: After fitting this cell, run the laptop on battery until it hibernates at cutoff — do not interrupt it. Then charge uninterrupted to 100%. This single cycle resets the BIOS battery learn sequence and clears the inaccurate health warning that appears immediately after any cell swap on Alienware hardware.

BIOS reporting battery health as poor after swapping in a new cell

The Alienware M15X stores battery health data in EEPROM on the original cell. When a new cell is installed, the BIOS reads that stored data as mismatched and flags a health warning — even though the new cell is physically fine. This is not a fault with the replacement; it is a firmware response to changed EEPROM values. Run one full discharge-to-hibernate cycle followed by an uninterrupted charge to 100% to force the BIOS to rewrite the learn cycle against the new cell. After two to three full cycles the health indicator should read normal.

Laptop shutting down at 20–30% shown on the gauge

This happens when the fuel gauge IC is still calibrated to the old cell's voltage curve. The gauge shows 25% remaining but the actual cell voltage has already dropped below the EC's cutoff threshold under full CPU and GPU load. The laptop shuts down because the real voltage — not the reported percentage — hit the floor. Run two full discharge-to-hibernate cycles without interrupting the charge, and the fuel gauge IC will recalibrate its curve against the new cell's actual voltage behaviour. After recalibration, shutdown should not occur above 5% reported charge.