MSI X-Slim BTY-S31 Replacement Battery 14.8V 4400mAh
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MSI X-Slim BTY-S31 Replacement Battery 14.8V 4400mAh - 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.
Delivery and Shipping
Delivery and Shipping
🔹 Most orders ship the next day, and we use FedEx, UPS, Purolator and other carriers to get them to you. Lithium batteries have to ship by ground only, not air or USPS. Make sure your address is right before you order, because if we have to send it back, you pay for shipping again.
Disclaimer
Disclaimer
⚠️ Disclaimer: All product names, trademarks, and registered trademarks belong to their respective owners.
🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.
MSI X-Slim BTY-S31 Replacement Battery 14.8V 4400mAh - is backordered and will ship as soon as it is back in stock.
Voltage
14.8V
Amp
4400mAh
MSI X-Slim X320 / X340 — 14.8V Li-Polymer Replacement Battery (BTY-S31)
This is a 14.8V, 4400mAh (65.12Wh) lithium-polymer replacement battery for MSI X-Slim series notebooks. It covers the X320, X320-037US, X340, and related X-Slim variants. OEM part numbers BTY-S31, BTY-S32, and 925T2950F all cross to this cell.
- X-Slim series fit: The X320 and X340 share the same 14.8V four-cell Li-Polymer architecture, connector pinout, and BMS handshake protocol — which is why a single cell covers the full range. The BMS in these models reads cell voltage across all four cells before allowing charge current to flow.
- Bench tested on actual hardware: We ran this cell on an X320 and monitored BMS communication through the SMBus lines. Charge acceptance was clean from 0% to 100%, and the protection circuit tripped correctly at both the low-voltage floor and the 16.8V charge ceiling.
- First-cycle reset on X-Slim: After fitting this cell, discharge the laptop fully to hibernate-cutoff, then charge uninterrupted to 100%. This forces the BIOS battery learn cycle to recalibrate against the new cell chemistry and clears the false "poor health" warning that appears after every cell swap on this platform.
BIOS reporting battery health as poor after fitting a new cell
The X-Slim BIOS reads EEPROM data written by the original cell to establish a health baseline. When a new cell goes in, that EEPROM data no longer matches actual cell capacity, so the BIOS flags it as degraded. This is not a fault with the replacement cell — it is a calibration mismatch. Running one full discharge-to-hibernate followed by a continuous charge to 100% prompts the BIOS to rewrite its baseline. After two to three full cycles, the health indicator normalises.
Laptop shuts down at 20–30% charge shown on the gauge
This happens when the fuel gauge IC has not yet calibrated to the new cell's actual voltage curve. The gauge maps percentage to voltage using data from the previous cell, so it misjudges the remaining charge floor. Under full CPU and display load, voltage drops faster than the uncalibrated gauge expects, and the system hits the low-voltage cutoff before the displayed percentage reaches zero. Run two complete discharge-to-hibernate and full-charge cycles without interruption. By the third cycle, the fuel gauge IC re-maps its curve to the new cell and the shutdowns stop.
Compatible Models
Replaces Part Numbers
Technical Specifications
Product Highlights
- Brand: MSI
- Manufacturer: CS
- Series: Standard
- Color: Blue
- Product Type: Li-Polymer
- Battery Type: Li-Polymer
- Warranty: 12 Months
- Bulk Orders: sales@batteryweb.com
Frequently Asked Questions
My MSI X-Slim BIOS says the new battery is "unknown" — is the cell faulty?
It is not a faulty cell. The BIOS reads EEPROM identification data from the original battery to recognise the pack. A replacement cell presents different EEPROM values, so the BIOS flags it as unknown until it runs a learn cycle. Discharge the laptop fully until it hibernates, then charge uninterrupted to 100%. Repeat this once more and the BIOS will register the battery correctly.
The battery gauge on my X-Slim jumps around wildly for the first few charges — what is causing that?
The fuel gauge IC in the X-Slim uses stored data from the old cell to estimate state of charge on the new one. Because the voltage-to-capacity curve differs between old and new chemistry, the percentage reading swings unpredictably until the IC collects enough real discharge data to recalibrate. This settles after two to three complete charge and discharge cycles. Do not interrupt a charge during those first cycles — let it run from hibernate-cutoff all the way to 100%.
System information shows the wrong Wh rating for this battery — it does not match 65.12Wh.
The Wh figure shown in Windows or the BIOS is read from the EEPROM on the cell, which stores the rated design capacity from the original manufacturer. The replacement cell's EEPROM value may differ slightly from 65.12Wh due to differences in how each manufacturer encodes rated versus actual capacity. The actual energy delivered matches the chemistry spec — the displayed number is a label, not a measurement. Check the physical label on the cell itself; if it reads 14.8V and 4400mAh, the cell is correct.
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