Asus VivoBook S14 C31N1821 Replacement Battery 11.55V
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Asus VivoBook S14 C31N1821 Replacement Battery 11.55V - is backordered and will ship as soon as it is back in stock.
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Battery Care Tips
Battery Care Tips
🔹 Getting Started
Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.
🔹 Keep It Healthy
Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.
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Delivery and Shipping
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Disclaimer
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🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.
Asus VivoBook S14 C31N1821 Replacement Battery 11.55V - is backordered and will ship as soon as it is back in stock.
Voltage
11.55V
Amp
4150mAh
Asus VivoBook S14 S433FA Series — 11.55V Li-Polymer Replacement Battery (C31N1821)
This is a 11.55V, 4150mAh (47.93Wh) Li-Polymer battery for the Asus VivoBook S14 S433FA-EB491 and a wide range of S433 series variants. It replaces OEM part numbers C31N1821, C31POJH, and 0B200-03210100. The three-cell flat-pack form factor fits flush inside the S14 chassis without modification.
- S433 series fitment: The S433FA, S433EA, and S433IA all run the same 11.55V three-cell Li-Polymer rail with an identical connector and BMS handshake protocol. That shared architecture is why one cell covers all those variants — the BIOS battery interface communicates the same way across the lineup.
- Bench tested on actual hardware: We ran this cell on an S433FA unit and confirmed the BMS initialised without fault codes. Charge acceptance was clean from 0V recovery through to the BIOS charge cutoff threshold, and the EC reported cell voltage within normal tolerance on all three cells.
- First-cycle reset on the S433 platform: After fitting, let the laptop discharge fully until it hibernates on its own, then charge it in one uninterrupted session to 100%. This forces the BIOS battery learn cycle to recalibrate against the new cell and clears the inaccurate health warning the EC throws after any cell swap.
BIOS reporting poor battery health immediately after fitting a new cell
The S433's embedded controller stores learned charge data from the previous cell in EEPROM. When a new cell goes in, that old data still sits in memory and the EC flags a health mismatch — sometimes showing "poor" status or an incorrect Wh rating before a single charge cycle runs. This is not a fault with the replacement cell. Running one full discharge-to-hibernate followed by an uninterrupted charge to 100% triggers the BIOS learn cycle and overwrites the stale EEPROM values. After two to three full cycles, the health readout in Windows Battery Report will normalise.
VivoBook S14 shuts off abruptly at 20–30% shown on the fuel gauge
This symptom points to a voltage cliff under combined CPU and display load — the cell can't sustain the voltage rail when current draw peaks, even though the fuel gauge still shows charge remaining. The fuel gauge IC on the S433 platform reads state-of-charge against a stored discharge curve, and if that curve hasn't been calibrated against the new cell, it reports capacity that isn't actually deliverable under load. Run two full calibration cycles — discharge to hibernate cutoff, then charge uninterrupted to 100% — and the fuel gauge IC will map its curve to the actual cell. Shutdowns at a false 20–30% should stop once the IC has accurate data to work from.
Compatible Models
Replaces Part Numbers
Technical Specifications
Product Highlights
- Brand: Asus
- Manufacturer: CS
- Series: Standard
- Color: Black
- Product Type: Li-Polymer
- Battery Type: Li-Polymer
- Warranty: 12 Months
- Bulk Orders: sales@batteryweb.com
Frequently Asked Questions
The VivoBook S14 shows the battery as "unknown" or 0% in Windows right after I put the new cell in — is the battery dead already?
No — the embedded controller still has EEPROM data from the old cell and hasn't recognised the new one yet. This is a calibration state, not a hardware fault. Run the laptop down until it hibernates on its own, then charge it to 100% in one uninterrupted session. After that full cycle, the EC re-initialises and Windows will report the correct state-of-charge.
My S433FA charges fine but the system info shows the battery's Wh rating as lower than what the replacement cell is rated for — why?
The Wh value displayed in Windows pulls from EEPROM on the battery controller, not a live measurement. The old cell's rated capacity is still stored there. After one to two full discharge-and-charge calibration cycles, the fuel gauge IC rewrites that value against the new cell's actual chemistry. Check the Wh figure again in Windows Battery Report after the second complete cycle — it should align with the 47.93Wh spec.
The replacement battery charges but stops at 80% and won't go higher — is there a setting I need to change?
This is the BIOS-controlled charge limit on Asus laptops, not a fault with the cell. Asus MyASUS has a Battery Health Charging mode that caps charge at 60% or 80% to reduce long-term cell stress. Open MyASUS, go to Customization, then Battery Health Charging, and switch the mode to Full Capacity. The battery will then charge to 100% on the next cycle.
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