About this replacement
Asus Transformer Flip TP550LA / TP550LD — 7.6V Li-Polymer Replacement Battery (C21N1333)
This 7.6V 5000mAh (38Wh) lithium-polymer battery replaces part number C21N1333 in the Asus Transformer Flip TP550LA and TP550LD convertible laptop-tablet. It also fits TP550LA-CJ127H, R554LA-RH31T, and related TP550 variants sharing the same connector and BMS handshake. Alternate OEM references include 0B200-00860000 through 0B200-00860400.
- TP550 series compatibility: The TP550LA and TP550LD share the same battery bay dimensions, 7.6V power rail, and two-pin SMBus connector. The BMS on both models negotiates state-of-charge data over the same protocol, so one cell fits both without hardware modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on a TP550LA and confirmed the BMS authenticated correctly, charge termination triggered at full capacity, and the SMBus returned accurate voltage readings throughout.
- First-cycle calibration on the TP550: After fitting this battery, run the laptop on battery power until it reaches hibernate-cutoff, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the false health warning that appears after every cell swap on this platform.
Why the TP550LA shuts down at 20–30% remaining after a battery swap
The TP550LA's fuel gauge IC builds its discharge model against the original cell's EEPROM data. A new cell has a different internal resistance profile, so the gauge loses accuracy at the low end of the charge curve. When the CPU and display pull full load, the cell voltage drops faster than the IC predicts, and the system cuts out before the gauge hits zero. Running two full discharge-to-hibernate cycles recalibrates the IC against the new cell's actual voltage curve and eliminates the premature shutdown.
BIOS reports battery health as poor or unknown immediately after installation
This happens because the BIOS reads health data from the old cell's EEPROM and compares it against what the new cell reports — the mismatch triggers a health warning even though the cell is new. It is not a fault with the replacement. Run the ASUS Battery Health Charging utility, let one complete charge cycle finish, and the BIOS will update its stored baseline. After that cycle, the health status clears and reports correctly.