About this replacement
Asus Transformer Book TX201LAF — 3.85V Li-Polymer Replacement Battery (C12N1343)
This is a 3.85V, 7900mAh (30.42Wh) Li-Polymer replacement battery for the Asus Transformer Book TX201LAF and TX201 series. These are hybrid 2-in-1 devices with a detachable touchscreen tablet portion and keyboard dock. The battery sits inside the display tablet unit and powers the system when undocked.
- TX201LAF and TX201 tablet unit fit: Both models share the same detachable display assembly, connector pinout, and BMS handshake protocol. The C12N1343 cell matches the OEM voltage rail and communicates correctly with the ASUS EC firmware over the SMBus line.
- Bench tested on actual hardware: We ran this cell through charge, discharge, and re-dock cycles on TX201 hardware. The BMS reported state of charge correctly to the OS, charge current tapered as expected at high SOC, and the EC did not flag an unrecognised cell error.
- First-cycle recalibration on the TX201: After installing, discharge the tablet fully until Windows hibernates at critical battery level, then charge uninterrupted to 100% without using the device. This forces the fuel gauge IC to map the new cell's capacity curve and clears the inaccurate health warning that appears after a cell swap.
Why the TX201LAF BIOS reports poor battery health immediately after replacement
The TX201LAF stores battery wear data in EEPROM on the original cell's BMS board. When a new cell is installed, the BIOS reads a fresh EEPROM with no cycle history and flags a mismatch against its stored baseline — showing "poor health" or "replace battery" even though the cell is new. This is a firmware reporting artefact, not a cell fault. Running one full discharge-to-hibernate then a full uninterrupted charge resets the BIOS battery learn cycle and clears the warning within one to two charge sessions.
TX201 shutting down at 20–30% battery shown on screen
This happens when the fuel gauge IC has not yet calibrated against the new cell's discharge curve. The old curve data still in firmware causes the reported percentage to drift from actual cell voltage, and the system hits the hardware low-voltage cutoff before the OS gauge reaches zero. The fix is a full calibration cycle: run the tablet on battery from 100% down to automatic hibernate, then charge fully without interruption. After two to three of these cycles the gauge tracks correctly and the early shutdowns stop. Check that resting cell voltage reads 3.85V or above after a full charge to confirm the cell is holding.