Asus Transformer 11.6 Replacement Battery C21N1504 7.6V 4750mAh

Asus Transformer TP200SA Series — 7.6V Li-Polymer Replacement Battery (C21N1504)

This is a 7.6V, 4750mAh (36.1Wh) Li-Polymer battery for the tablet portion of the Asus Transformer 11.6 detachable hybrid. It fits the TP200SA, TP200SA3050, E205SA, and related models. When the original cell degrades, the tablet unit loses portability — this cell restores it.

• TP200SA platform compatibility: These models share the same 7.6V two-cell Li-Polymer configuration, connector pinout, and BMS handshake protocol — which is why one part number covers the full TP200SA family without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a TP200SA unit. The BMS accepted the new cell without fault codes, the fuel gauge IC initialised correctly, and charge progression through the CC/CV curve was normal on both cycles we ran.
• First-cycle recalibration on the TP200SA: After fitting, let the tablet discharge fully until it hibernates, then charge uninterrupted to 100%. This forces the fuel gauge IC to map its thresholds against the new cell and clears the inaccurate health warning the BIOS throws after every cell swap.

BIOS reporting poor battery health immediately after fitting the C21N1504

The Asus BIOS reads health data from the battery's EEPROM, which stores cycle count and rated capacity from the previous cell. A new cell arrives with its own EEPROM data, and the BIOS flags a mismatch as degraded health before any calibration has run. This is not a fault with the replacement cell — it is the firmware interpreting fresh EEPROM data against a stored baseline. Run one full discharge-to-hibernate followed by an uninterrupted charge to 100%. After that cycle, the BIOS health indicator updates to reflect the actual cell condition.

Transformer tablet shutting down at 20–30% shown on the charge indicator

This happens when the fuel gauge IC has not yet calibrated its voltage-to-capacity curve against the new cell. Under combined CPU and display load, the cell voltage drops faster than the uncalibrated gauge expects, and the protection circuit cuts power before the display shows 0%. It looks like an early shutdown but is a mapping error, not a capacity fault. Run two full discharge-to-hibernate and charge-to-100% cycles — after the second cycle, the gauge IC recalibrates its lower voltage threshold and the shutdowns stop.