About this replacement
Asus VivoBook Flip TP501 Series — 7.6V Li-Polymer Replacement Battery (C21N1518)
This is a 7.6V, 4000mAh (30.4Wh) Li-Polymer battery for the Asus VivoBook Flip TP501, TP501UA, TP501UB, and TP501UQ. It replaces OEM part numbers C21N1518 and 0B200-01850000. If your original cell holds a fraction of its original charge or won't register in Windows at all, this swap restores full portable operation on that 2-in-1 convertible.
- TP501 series compatibility: The TP501UA, TP501UB, and TP501UQ all share the same battery bay geometry, connector pinout, and 7.6V nominal rail. The BMS handshake uses the same two-wire SMBus protocol across the full range, so one cell covers all four variants without modification.
- Bench tested on actual hardware: We cycled this cell on a TP501UB unit and confirmed the BMS negotiated charge cutoff correctly at 8.7V and discharged to the 6.0V low-cell protection threshold without false trips or thermal events.
- Post-swap BIOS learn cycle: After fitting this battery, run the laptop on battery alone until it hibernates at the low-voltage cutoff — 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 TP501 BIOS reports poor battery health immediately after a new cell install
The TP501 stores learned capacity data in EEPROM on the battery's fuel gauge IC. When you swap the cell, the BIOS reads stale EEPROM values from the new pack — often flagging it as degraded before a single charge cycle completes. This is not a fault with the replacement cell. The BIOS health indicator only resets after the fuel gauge IC logs enough real-world charge and discharge data to overwrite its initial estimate. One full discharge-to-hibernate followed by an uninterrupted full charge is usually enough to clear the warning.
TP501 shutting down at 20–30% battery shown on screen
This happens when the fuel gauge IC hasn't yet calibrated against the new cell's actual voltage curve. The displayed percentage is calculated from old EEPROM data, so the reported 25% can correspond to a real cell voltage already near the 6.0V cutoff. Under combined CPU and touchscreen load the voltage drops faster than the gauge predicts, and the BMS trips the circuit before the OS can log a low-battery warning. Run two full discharge-to-hibernate then full-charge cycles — after that the fuel gauge tracks the real voltage curve and the shutdowns stop.