About this replacement
Asus VivoBook S200 Series — 7.4V Li-Polymer Replacement Battery (C21-X202)
This is a 7.4V, 5100mAh (37.74Wh) Li-Polymer replacement battery for the Asus VivoBook S200 family of 11.6-inch touchscreen ultrabooks. It fits the S200, S200L3217E, S200L987E, X202E, and over 165 additional VivoBook variants sharing the C21-X202 form factor. OEM part numbers covered include C21-X202, 0B200-00230300, and C22-X202.
- VivoBook S200 and X202E platform fit: These models share a unified battery bay spec — same 246.90 × 80.95 × 6.40mm slim-pack footprint, same two-cell 7.4V Li-Polymer configuration, and the same SMBus connector pinout. Any variant in this cluster that accepts C21-X202 will accept this cell.
- Bench tested on actual hardware: We ran this cell on an X202E motherboard and monitored BMS communication across a full charge cycle. The protection circuit responded correctly to charge termination, temperature thresholds, and over-discharge cutoff without throwing error flags in the EC firmware.
- Post-install calibration on the VivoBook S200: After fitting this cell, run the battery down fully until the laptop enters hibernate, then charge uninterrupted to 100% before rebooting. This forces the embedded controller to re-learn the new cell's capacity curve and clears the inaccurate health warning that appears in MyASUS or Windows after any cell swap.
BIOS reporting battery health as poor immediately after swap
The VivoBook S200 stores battery wear data in EEPROM on the old cell. When a new cell goes in, the embedded controller reads no cycle history and flags the battery as degraded or unknown — this is a data mismatch, not a fault with the replacement. The BIOS health indicator will not self-correct until the EC completes at least one full learn cycle. Run the battery from 100% down to hibernate cutoff and back to full charge without interruption. After one complete cycle, the health status in BIOS and MyASUS will update to reflect the actual new cell state.
Laptop shuts off at 20–30% charge shown on the gauge
This is a voltage cliff symptom — the fuel gauge IC is still reading calibration data mapped to the old, worn cell. The new cell's actual voltage drop under CPU and display load hits the EC's low-voltage cutoff threshold before the percentage gauge reaches zero. The gauge and the real cell state are out of sync. Complete two full discharge-to-hibernate and charge-to-100% cycles back-to-back; this gives the fuel gauge IC enough data points to remap the discharge curve against the new cell's actual 7.4V chemistry and eliminate the premature shutdown.