Asus UX561UD Replacement Battery 11.52V 3600mAh Li-Polymer

Asus UX561UD / Q535UD Series — 11.52V Li-Polymer Replacement Battery (C31N1704)

This is an 11.52V, 3600mAh (41.47Wh) lithium-polymer battery that replaces the original C31N1704 / 0B200-02650000 unit in the Asus VivoBook 15 X561UD and ZenBook Flip UX561UD. It fits the Q535U and Q535UD lines as well, including the Q535UD-BI7T11. When the factory cell degrades or stops holding charge, this restores full cordless operation to the laptop.

• UX561UD / Q535UD platform fit: These models share the C31N1704 cell format — same 3-cell Li-Polymer configuration, same connector pinout, and same BMS handshake protocol. The voltage rail at 11.52V nominal matches what the EC firmware expects during charge negotiation.
• Bench tested on actual hardware: We ran this cell on a UX561UD board and confirmed the BMS handshake completed without fault codes. Charge acceptance was normal from flat through to full, with no thermal events or premature cutoff under combined CPU and display load.
• BIOS learn cycle after install: After fitting this battery, run the laptop down to hibernate-cutoff on a real workload, then charge uninterrupted to 100%. This forces the fuel gauge IC to recalibrate against the new cell's actual capacity and clears the inaccurate health warning that appears in MyASUS or BIOS after any cell swap.

BIOS reporting poor battery health immediately after fitting a new cell

The UX561UD stores battery health data in EEPROM on the old cell's BMS board. When a new cell is fitted, the EC reads that the cycle count and capacity data don't match the fresh chemistry, so it flags poor health or "replace battery" straight away. This is not a fault with the new cell — it's stale EEPROM data misleading the firmware. One full discharge-to-hibernate followed by an uninterrupted charge to 100% forces the EC to rewrite its baseline. After two to three complete cycles the health indicator stabilises.

Laptop shuts down at 20–30% charge shown on the gauge

This usually happens in the first few cycles after a swap, before the fuel gauge IC has calibrated against the new cell. The gauge reads 25% but the cell voltage has already dropped below the EC's shutdown threshold — typically around 10.0V under full CPU plus display load. The controller cuts power before the reported percentage reaches zero, which looks like a sudden shutdown. Run two complete discharge and recharge cycles without interrupting the charge, and the gauge will align the cutoff point accurately to the new cell's actual voltage curve.