About this replacement
Asus VivoBook S551L Series — 11.1V Li-Polymer Replacement Battery (C31-S551)
This 11.1V, 4500mAh Li-Polymer battery replaces the OEM C31-S551 cell in the Asus VivoBook S551L, S551LA, and S551LB notebooks. It fits the ultrabook-style chassis without modification and connects via the original three-cell connector. Capacity is 4500mAh (49.95Wh) — matching the stock specification.
- S551L platform fit: The S551L, S551LA, and S551LB share the same 11.1V three-cell Li-Polymer architecture, connector pinout, and BMS handshake protocol. One cell covers all three variants because the voltage rail and communication interface are identical across the platform.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on the S551LB platform. The BMS negotiated correctly with the ASUS EC firmware — no charging errors, no ACPI fault codes, and the fuel gauge updated continuously through each cycle.
- Post-install calibration for the S551L: After fitting this cell, run the laptop down to hibernate cutoff under normal use — screen on, applications running — then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap on this platform.
Why the S551L BIOS reports poor battery health after a cell swap
The S551L stores capacity history and cycle count data in the battery's EEPROM. When a new cell goes in, that EEPROM is blank or carries factory defaults the BIOS does not recognise as current. The embedded controller reads this as a degraded or unknown cell and flags poor health immediately. Running one full discharge-to-hibernate then an uninterrupted full charge writes new baseline data to the EEPROM and clears the flag. After two to three cycles the health reading stabilises to accurate.
Laptop shuts down at 20–30% charge shown on the S551L
This happens when the fuel gauge IC has not yet calibrated against the new cell's voltage curve. The old cell's curve is still cached, so the OS shows 25% while the actual cell voltage has already dropped below the safe cutoff threshold under CPU and display load. The laptop shuts down to protect the cell — not because the battery is faulty. Run two full discharge-to-hibernate cycles followed by uninterrupted full charges, and the fuel gauge IC recalibrates to the new cell. The cutoff point drops back to below 5% reported charge.