About this replacement
Asus UX30KU / UX30 Series — 11.1V Li-Polymer Replacement Battery (C31-UX30)
This is an 11.1V, 3250mAh (36.08Wh) lithium-polymer replacement battery for the Asus UX30KU ultrabook and the broader UX30 family, including the UX30, UX30KA, and UX30-a1. It uses OEM part numbers C31-UX30, 70-NVS1B1000Z, and PP625289AB-3250. The cell slots into the same bay and connects to the same BMS circuitry as the original.
- UX30 family compatibility: The UX30, UX30KU, UX30KA, and UX30-a1 all share the same 11.1V three-cell Li-Polymer pack architecture, the same physical connector, and the same BMS handshake protocol — so one cell services the entire line without modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on UX30-series hardware. The BMS accepted the pack, communicated state-of-charge correctly to the OS, and held voltage across load without tripping the protection circuit.
- First-cycle recalibration on the UX30KU: After fitting this battery, run one full discharge to hibernate-cutoff, then charge uninterrupted to 100%. This forces the BIOS to complete its battery learn cycle against the new cell and clears the inaccurate health warning that appears after every cell swap on this platform.
Why the UX30KU BIOS flags poor battery health after a cell swap
The UX30KU stores battery state data — cycle count, charge history, and health rating — in EEPROM on the old cell's fuel gauge IC. When you fit a new pack, the BIOS reads stale EEPROM data and reports poor health even though the cell is fresh. This is not a fault with the replacement. Running the full discharge-to-hibernate then uninterrupted charge cycle forces the BIOS learn algorithm to overwrite that stale data with real readings from the new cell. After one or two complete cycles, the health flag clears and the fuel gauge reads accurately.
UX30KU shutting down at 20–30% charge remaining
This happens when the cell voltage drops below the BMS cutoff threshold under full CPU and display load — even though the OS gauge still shows charge remaining. The fuel gauge IC has not yet calibrated against the new cell's actual voltage curve, so the percentage shown does not match the real state of charge. The fix is the same recalibration cycle: discharge fully to hibernate, then charge to 100% without interruption. After two complete cycles the gauge aligns to the cell and the early shutdown stops.