About this replacement
Asus Transformer Book T300FA — 7.6V Li-Polymer Replacement Battery (C21N1413)
This is a 7.6V 3900mAh (29.64Wh) Li-Polymer battery for the Asus Transformer Book T300FA convertible notebook. It replaces OEM part C21N1413 and fits the T300FA-FE001H, T300FA-DH12T-CA, and T300FA-DH12 variants. The T300FA is a detachable two-in-one — this cell sits in the tablet portion of the chassis and powers the full unit whether the keyboard dock is attached or not.
- T300FA tablet unit compatibility: All T300FA variants share the same tablet chassis, voltage rail, and BMS connector layout. The C21N1413 is the only cell Asus specified for this chassis. Voltage and pack dimensions must match exactly — the 218.24 x 127.67 x 3.12mm profile leaves no clearance for deviation.
- Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on a T300FA unit. The BMS handshake completed correctly, charge termination triggered at 100%, and no overcurrent trips occurred during display-plus-CPU load testing.
- Post-install calibration on the T300FA: After fitting, run the tablet down to hibernate cutoff, then charge uninterrupted to 100% without using the device. This resets the BIOS battery learn cycle. Skipping this step causes the OS fuel gauge IC to read the new cell's EEPROM incorrectly and report inaccurate charge levels for the first several sessions.
Why the T300FA shuts down at 20–30% charge remaining
This is a voltage cliff failure, not a fuel gauge error. As a Li-Polymer cell ages, it loses the ability to hold voltage under combined CPU and display load — even when the gauge still reads 25%. The BMS reads the voltage drop as a safe-shutdown threshold breach and cuts power immediately. A new cell with full capacity restores the flat discharge curve, so voltage stays above the BMS cutoff point through the lower charge range. If shutdowns persist after fitting a new cell, run the full calibration cycle first before concluding a fault.
BIOS reporting new battery health as poor or unknown after swap
The BIOS reads health data from the old cell's EEPROM during every boot — after a swap, it compares the new cell against the stored wear profile and flags a mismatch as degraded or unknown. This is not a fault with the replacement cell. Run one full discharge-to-hibernate then a full uninterrupted charge to 100%. This forces the BIOS battery learn cycle to write a fresh baseline to EEPROM and clears the health warning on the next boot.