Asus ZenBook UX51 C42-UX51 Replacement Battery 14.8V 4750mAh

Asus ZenBook UX51 Series — 14.8V Li-Polymer Replacement Battery (C42-UX51)

This is a 14.8V, 4750mAh (70.3Wh) Li-Polymer battery pack for the Asus ZenBook UX51 and U500VZ ultrabook lineup. It fits the ZenBook UX51VZ, U500VZ-CN032H, and the broader UX51 and U500VZ family. Install it when the original cell no longer holds enough charge for portable use.

• UX51 and U500VZ platform fitment: These models share the same 14.8V four-cell Li-Polymer architecture, identical connector pinout, and the same BMS communication protocol over the SMBus rail — which is why one cell part number covers the full UX51 and U500VZ range.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on UX51VZ hardware. The BMS handshake completed correctly, the SMBus reported accurate state-of-charge data, and the charge controller reached full cutoff without fault flags.
• First-cycle calibration on the UX51: After fitting, run the laptop on battery until it hibernates at low charge, then charge uninterrupted to 100%. This forces the UX51's fuel gauge IC to recalibrate against the new cell and clears the inaccurate health warning that appears in BIOS after every cell swap.

BIOS reporting poor battery health immediately after fitting the C42-UX51

The ZenBook UX51 stores battery health data in EEPROM on the old cell. When a new cell is fitted, the BIOS compares live SMBus readings against that stale EEPROM baseline and flags a mismatch as poor health. This is not a fault with the replacement cell — it is a data conflict. Running one full discharge-to-hibernate followed by a complete uninterrupted charge resets the learn cycle. After two to three full cycles, the BIOS health reading normalises.

UX51 shuts down at 20–30% charge shown on screen

This happens when the fuel gauge IC has not yet calibrated against the new cell's actual voltage curve. The gauge reads 20–30% remaining, but the cell has already dropped below the minimum voltage the CPU and display load can sustain — causing an abrupt shutdown. The fix is the same calibration cycle: discharge fully to hibernate cutoff, then charge to 100% without interruption. After two cycles the gauge tracks accurately and shutdowns at false percentages stop. Confirm calibration is complete by checking that the reported voltage at full charge sits at or above 16.6V in a battery utility.