Asus EeeBook E402MA Replacement Battery 11.4V B31N1425

Asus EeeBook E402MA — 11.4V Li-Polymer Replacement Battery (B31N1425)

This 11.4V, 4100mAh (46.74Wh) lithium-polymer cell replaces the original B31N1425 battery in the Asus EeeBook E402MA series. It fits the E402MA, E402MA-WX0018H, E402MA-WX0001H, and related variants. The connector, BMS pinout, and physical dimensions match the OEM spec at 211.15 x 166.72 x 6.70mm.

• E402MA series fit: All E402MA variants share the same 11.4V three-cell Li-Polymer configuration, B31N1425 part number, and BMS handshake protocol — so one cell covers the full model range without modification.
• Bench tested on actual hardware: We ran this cell on the E402MA platform and confirmed the BMS completed charge handshake with the EC, reported state-of-charge correctly in BIOS, and held voltage above the low-battery cutoff threshold under combined CPU and display load.
• First-cycle reset on the E402MA: After fitting, run the laptop on battery until it hibernates at the low-charge cutoff, then charge uninterrupted to 100%. This forces the BIOS battery learn cycle to reset against the new cell and clears the inaccurate health warning that appears after every cell swap on this platform.

Why the E402MA BIOS reports poor health immediately after a battery swap

The E402MA stores learned battery data — cycle count, calibrated capacity, and health state — in EEPROM on the embedded controller. When a new cell is fitted, the EC reads stale data from the old session and flags the battery as degraded before a single charge cycle completes. This is not a fault with the replacement cell. Running one full discharge-to-hibernate followed by an uninterrupted charge to 100% triggers the BIOS learn cycle, writes fresh capacity data to the EC, and clears the health warning. After two to three cycles the fuel gauge IC will report accurate state-of-charge.

E402MA shutting down at 20–30% charge shown on screen

This symptom points to a voltage cliff in the cell — the pack voltage drops sharply under combined CPU and display load before the fuel gauge reaches zero. The EC triggers a protection shutdown when cell voltage falls below roughly 9.0V (3.0V per cell), even if the OS still shows charge remaining. The fuel gauge IC has not yet calibrated against the new cell's actual discharge curve. Run two full discharge-to-hibernate cycles charging to 100% each time — after calibration the gauge and the actual cutoff voltage will align and early shutdowns will stop.