About this replacement
Asus Vivobook S 14 OLED K3402ZA Series — 11.61V Li-Polymer Replacement Battery (C31N2105)
This is a 11.61V, 5800mAh (67.34Wh) Li-Polymer battery for the Asus Vivobook S 14 OLED K3402ZA-AOQ25031W and a wide range of compatible Vivobook 14 and 15 OLED models. OEM part numbers C31N2105 and 0B200-04140000 confirm fitment. It replaces cells that have degraded, lost hold capacity, or no longer power the laptop off AC.
- Vivobook S 14/15 OLED platform fitment: The K3402ZA, X1403ZA, M3402QA, and K3502ZA share the same 11.61V three-cell Li-Polymer architecture, connector pinout, and BMS communication protocol — one cell services all of them without modification.
- Bench tested on actual hardware: We ran the C31N2105 cell through full charge cycles on the Vivobook platform and monitored BMS handshake data. The protection circuit responded correctly to charge termination and low-voltage cutoff thresholds at each stage.
- Post-install recalibration cycle: After fitting this cell, discharge the laptop fully until it hibernates, then charge uninterrupted to 100% without removing the AC adapter. 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.
Why the Vivobook BIOS reports poor battery health immediately after a cell swap
The Vivobook firmware stores battery health data in EEPROM tied to the original cell's charge history. When a new cell is installed, the BIOS reads that stored data and flags the battery as degraded — because the cycle count and capacity figures no longer match the physical cell. This is a firmware read issue, not a fault with the replacement. Running one full discharge-to-hibernate followed by an uninterrupted charge to 100% triggers the BIOS learn cycle and overwrites the stale EEPROM values. After two to three full cycles, the health readout in Windows and the BIOS will reflect the actual capacity of the new cell.
Laptop shuts down at 20–30% remaining after battery swap
This happens when the fuel gauge IC has not yet calibrated against the new cell's actual voltage curve. The gauge maps percentage to voltage using data from the old, degraded cell — so it hits the low-voltage cutoff point earlier than the display suggests. Under combined CPU and OLED panel load, the cell voltage drops faster than the uncalibrated gauge anticipates, triggering a shutdown. Run two full discharge cycles from 100% down to hibernate cutoff, charging fully between each run. By the second cycle the fuel gauge IC recalibrates, and shutdown should not occur above 10–12% under normal load.