About this replacement
Asus R2H / R2E / R2Hv — 7.4V Li-Polymer Replacement Battery (C21-R2)
This is a 7.4V, 3430mAh (25.38Wh) lithium-polymer replacement battery for the Asus R2H, R2E, and R2Hv convertible tablet-laptop. The C21-R2 fits the slim battery bay on all three variants with the original connector orientation and BMS pinout. Install it as a direct swap when the original cell no longer holds a useful charge.
- R2H, R2E, and R2Hv compatibility: All three models share the same battery bay dimensions, 7.4V two-cell architecture, and BMS handshake protocol — that is why one part number covers the whole R2 line. The connector and locking tab are identical across the series.
- Bench tested on actual hardware: We cycled this cell through full charge-discharge sequences and confirmed the BMS communicates charge state correctly to the host system. Capacity read-back at 3430mAh matched product spec within normal cell tolerance.
- Post-install calibration for the R2H: After fitting, run the tablet to hibernate-cutoff on battery only, then charge uninterrupted to 100% without waking the device. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap on the R2 platform.
BIOS reporting poor battery health immediately after fitting the C21-R2
The R2H BIOS reads health data from the battery's EEPROM, which stores cycle count and rated capacity from the previous cell. A new cell ships with factory EEPROM defaults that do not match your system's logged history, so the BIOS flags a mismatch as poor health. This is a data conflict, not a fault with the replacement cell. Run one full discharge-to-hibernate followed by an uninterrupted charge to 100% to let the BIOS rewrite its battery learn table against the new cell's actual readings. After two or three cycles the health indicator should normalise.
Fuel gauge jumping erratically for the first few charge cycles
The fuel gauge IC in the R2H calibrates its internal model against the specific impedance curve of the installed cell. Swap the cell and that model is mismatched — the gauge can read 60% one moment and drop to 35% shortly after under light load. This is not a defective battery; it is the IC recalculating against unfamiliar cell data. Run two or three full discharge-to-charge cycles without interrupting the charge phase and the gauge IC will rebuild an accurate model. After the third cycle, readings should track linearly from 100% down to the hibernate cutoff near 3.0V per cell.