Asus C21N1423 Replacement Battery 7.6V 4900mAh

Asus R301UA / X302UA Series — 7.6V Li-Polymer Replacement Battery (C21N1423)

This is a 7.6V 4900mAh (37.24Wh) Li-Polymer battery for the Asus VivoBook R301UA, R301UV, R301LJ, X302UA, and related 13.3-inch notebook models. It replaces OEM part numbers C21N1423 and 0B200-01360100. If your original cell has degraded, stopped holding charge, or the laptop runs only on AC power, this is the direct cell swap.

• R301 and X302 series compatibility: These models share the same two-cell Li-Polymer configuration, 7.6V nominal rail, and the same BMS connector pinout. The battery management handshake is identical across the R301UA, R301UV, R301LJ, and X302UA variants, so one cell fits all.
• Bench tested on actual hardware: We ran this cell on an R301UA and monitored the BMS through charge and load cycles. The protection circuit triggered correctly at low-voltage cutoff and the charge IC accepted full current from cold start without throttling.
• Post-install calibration on VivoBook BIOS: After fitting this cell, run the laptop down to hibernate cutoff on battery power alone, then charge uninterrupted to 100% without disconnecting. This single learn cycle resets the BIOS fuel gauge against the new cell chemistry and clears the inaccurate health warning that appears after every cell swap on this platform.

Why the R301UA BIOS reports poor battery health immediately after a cell swap

The VivoBook BIOS stores battery health data in EEPROM on the original cell's BMS board. When a new cell is fitted, the BIOS reads the fresh EEPROM as mismatched against its stored baseline and flags the battery as degraded or unknown. This is not a fault with the replacement cell. One full discharge-to-hibernate followed by an uninterrupted charge to 100% forces the BIOS to rewrite its learned capacity baseline against the new cell, and the health warning clears on the next boot.

Laptop shuts down at 20–30% charge shown on screen

This happens when the fuel gauge IC has not yet calibrated to the new cell's actual voltage curve. The OS reads 25% remaining, but the cell voltage has already dropped below the BMS cutoff threshold under combined CPU and display load — so the system cuts power before the gauge catches up. It is not a defective cell. Run two full discharge-to-hibernate cycles with the display at full brightness and the laptop under moderate load, then recharge to 100% each time. After the second cycle, the fuel gauge IC recalibrates and the shutdown-at-30% behaviour stops.