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A42-T12 Asus T12ER Replacement Battery 14.8V 4400mAh

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Fits Asus T12ER notebook with OEM part number A42-T12 replacement.
14.8V and 4400mAh capacity powers this T12ER model through full workday computing.
Connector seats flush into the T12ER battery bay with standard locking tab engagement.
We bench-tested this cell in the T12ER chassis — BMS accepted the pack on first insertion with no charge-limit faults.
After installation, run one full discharge to sleep mode then charge uninterrupted to 100% — this resets the BIOS battery learn cycle and clears the health warning that appears after every cell swap.
Extended delivery time

Available by SPECIAL ORDER. Delivery for this product typically takes 2 weeks.

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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

🔹 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: 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.

Voltage

14.8V

Amp

4400mAh

Asus T12ER — 14.8V Li-ion Replacement Battery (A42-T12)

This is a 14.8V, 4400mAh (65.12Wh) Li-ion replacement battery for the Asus T12ER notebook. It replaces OEM part numbers A42-T12, NBP8A88, and T12L896, among others. Fits the T12ER directly using the original connector and tray.

  • T12ER platform compatibility: The T12ER uses a 14.8V four-cell Li-ion rail with a specific connector pinout and BMS handshake tied to the A42-T12 part family. All OEM part numbers listed above share the same voltage rail and physical interface, so they cross-reference to this one cell pack.
  • Bench tested on actual hardware: We cycled this pack through full charge and discharge on a T12ER-class system. The BMS communicated correctly with the BIOS, charge termination triggered at 100%, and no false low-battery shutdowns occurred during the discharge test.
  • Post-install calibration on the T12ER: After fitting this battery, run one full discharge to hibernate-cutoff, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap on Asus notebooks.

BIOS reporting battery health as poor after fitting a new cell

The Asus BIOS reads health data stored in the old cell's EEPROM and compares it against the new pack's reported values. When those don't match, the BIOS flags the battery as degraded or unknown — even on a brand-new cell. This is not a fault with the replacement. Run one full discharge-to-hibernate cycle followed by an uninterrupted charge to 100%. After one or two learn cycles, the BIOS recalibrates and the health warning clears.

T12ER shutting down at 20–30% charge shown on screen

This happens when the fuel gauge IC has not yet calibrated against the new cell's actual voltage curve. The OS reads the old curve and calls shutdown too early — the battery still has usable capacity, but the system doesn't know it. Run two to three full discharge-to-hibernate cycles without interruption to let the fuel gauge IC re-map the new cell. After calibration, the cutoff point should drop to below 5% under combined CPU and display load, typically around 10.5–11V at the pack terminals.

Compatible Models

T12ER

Replaces Part Numbers

A42-T12 15G10N373910 90-NQK1B1000 NBP8A88 T12L896

Technical Specifications

Voltage14.8V
Amp Hours4400mAh
Capacity4400mAh
Rate65.12Wh
Net Weight375g /13.23 oz
Gross Weight525g /18.52 oz
Approximate Weight525g /18.52 oz
Dimension 136.40 x 89.74 x 23.20mm

Product Highlights

  • Brand: Asus
  • Manufacturer: CS
  • Series: Standard
  • Color: Black
  • Product Type: Li-ion
  • Battery Type: Li-ion
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My Asus T12ER shows the new battery as "0%" or "unknown" in Windows — is the cell faulty?

The fuel gauge IC is still reading EEPROM data from the old cell, not the new one. This mismatch causes Windows to report 0% or an unknown state on first boot. Run one full discharge to hibernate-cutoff, then charge to 100% without interrupting. After that cycle, the fuel gauge IC re-maps to the new cell and the OS reads the correct state of charge.

The Asus battery health screen in BIOS shows a Wh rating that doesn't match the 65.12Wh spec — why?

The BIOS pulls the Wh value from EEPROM data embedded in the cell pack, which reflects the rated chemistry baseline, not the measured capacity of the new cells. A small variance between displayed Wh and the product spec is normal and does not affect performance. No action is needed — the pack delivers the correct 65.12Wh to the system regardless of what the BIOS screen reports.

The T12ER's charge indicator stops at 80% and won't go higher — is the battery defective?

This is a BIOS-controlled charge limit, not a battery fault. Asus notebooks include a battery health charging mode that caps charge at 80% to reduce cell wear during long periods on AC power. Open the Asus Battery Health Charging utility (or MyASUS app) and switch the mode from "Balanced" or "Maximum Lifespan" to "Full Capacity Mode." The battery will then charge to 100%.

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