Asus R2H Replacement Battery C21-R2 7.4V 3430mAh
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Asus R2H Replacement Battery C21-R2 7.4V 3430mAh - 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
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🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.
Asus R2H Replacement Battery C21-R2 7.4V 3430mAh - is backordered and will ship as soon as it is back in stock.
Voltage
7.4V
Amp
3430mAh
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.
Compatible Models
Replaces Part Numbers
Technical Specifications
Product Highlights
- Brand: Asus
- Manufacturer: CS
- Series: Standard
- Color: Metallic Grey
- Product Type: Li-Polymer
- Battery Type: Li-Polymer
- Warranty: 12 Months
- Bulk Orders: sales@batteryweb.com
Frequently Asked Questions
The R2H shuts down without warning while the battery gauge still shows 20–25% — what causes that?
The fuel gauge IC maps percentage to an old cell's voltage curve. A fresh cell hits its voltage cliff — where voltage drops sharply under CPU and display load — at a higher state of charge than the gauge expects, triggering an abrupt shutdown. The gauge is reading percentage against the wrong discharge curve. Run two full discharge-to-hibernate cycles on the new C21-R2, then recharge to 100% each time without interruption. After calibration, the gauge recalculates the cliff point correctly and the early shutdowns stop.
System information shows the wrong Wh rating after fitting the C21-R2 — it does not match 25.38Wh — is the battery faulty?
The Wh figure shown in Windows or the BIOS is pulled from the EEPROM data stored on the battery controller, not measured in real time. The EEPROM on a new cell ships with factory-programmed values that may differ slightly from the actual chemistry rating until the learn cycle completes. The physical cell capacity is not affected by what the EEPROM reports. Run a full discharge-to-hibernate followed by an uninterrupted charge to 100% and the system will rewrite the EEPROM entry against actual measured energy throughput.
The C21-R2 stops charging at around 80% and will not go higher — is the charge limit a BIOS setting or a battery fault?
On the R2 platform, some BIOS versions include a charge limit feature that caps charging at 80% to reduce cell stress during long AC-connected use. Check the BIOS Power Management page — look for a setting labelled "Battery Charge Limit" or "Maximum Battery Charge" and set it to 100%. If no such setting exists, confirm the AC adapter output is stable at 19V; a marginal adapter can cause the BMS to throttle the charge current and stop short of full capacity.
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