About this replacement
Asus ZenBook Flip 13 UX370UA — 7.7V Li-Polymer Replacement Battery (C21N1706)
This 7.7V, 4900mAh (37.73Wh) lithium-polymer cell replaces the original C21N1706 battery in the Asus ZenBook Flip 13 UX370UA series. It fits the convertible ultrabook across multiple UX370UA configurations including the 0061A7500U, C4124T, C4305T, C4178T, and 41 additional variants. Voltage, connector pinout, and BMS communication match the OEM spec exactly.
- UX370UA series compatibility: Every UX370UA variant in this fit list runs the same 7.7V dual-cell Li-Polymer architecture with identical connector orientation and BMS handshake protocol — that is why one cell covers the full model range without modification.
- Bench tested on actual hardware: We ran this cell in a UX370UA chassis and confirmed the BMS negotiated charge current correctly at startup, held the 7.7V rail stable under simultaneous CPU and display load, and triggered protection cutoff at the expected low-voltage threshold.
- First-cycle reset after installation: After fitting the new cell, run the laptop down until it hibernates on low battery, then charge uninterrupted to 100% without waking the device. This forces the BIOS battery learn cycle to rewrite its capacity baseline against the new cell and clears the inaccurate health warning that almost always appears after a cell swap.
Why the UX370UA shuts down at 20–30% after a battery swap
The ZenBook Flip's BIOS uses stored discharge curves from the old cell to predict the voltage cliff — the point where cell voltage drops sharply under load. With a new cell those curves are wrong, so the system panics and shuts down well above actual depletion. The new cell cannot sustain the combined voltage demand of the Intel Core processor and the 13.3-inch display at the same threshold the old degraded cell used. Running two full discharge-to-hibernate and uninterrupted charge cycles recalibrates the fuel gauge IC against the new cell's actual curve. After calibration, the shutdown threshold should stabilise at or below 5% remaining.
BIOS reporting battery health as "poor" or "replace" immediately after fitting
The BIOS reads health status from EEPROM data written by the previous cell's charge controller — not from the new cell's actual condition. A freshly installed cell with no cycle history looks "unknown" or degraded to the firmware until it completes a learn cycle. This is not a fault with the replacement cell. Boot into MyASUS or run the Windows Battery Report (powercfg /batteryreport) after completing one full discharge-charge cycle — the reported design capacity should align within 5% of 37.73Wh.