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Lenovo ThinkPad T420s Replacement Battery 11.1V 3600mAh 0A36287

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From $113.99 USD $136.99
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Replaces Lenovo OEM part numbers 0A36287, 42T4844, 42T4845, 42T4846, 42T4847, 45N1036, and 45N1037 for ThinkPad T420s, T420si, and T420s 4171-A13 laptops.
This 11.1V 3600mAh cell delivers 39.96Wh to sustain CPU and display load across a full workday without throttling.
Connector seats flush into the T420s battery slot with standard locking tab; no adapter needed for secure seating.
We bench-tested this pack against the original T420s platform — BMS accepted the new cell on first insertion with clean handshake, no fault codes.
After installation, run one full discharge cycle to hibernation 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.
Delivery time

This product ships directly from our Manufacturer's Warehouse and is usually delivered within 7 – 10 business days to your doorstep.

Discount: As a thank you for your patience, enjoy 5% off on your order
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Fresh Battery, Worth the Wait

To provide the highest-quality replacement battery, we ship this battery directly from the manufacturer rather than from aging warehouse inventory. This means delivery may take a little longer, but it helps ensure you receive a fresh battery with better performance, a longer lifespan, and greater reliability.

Estimated delivery: 7–10 business days
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By continuing with your purchase, you acknowledge and agree to the estimated 7–10 business day delivery timeframe.
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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.

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⚠️ 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

11.1V

Amp

3600mAh

Lenovo ThinkPad T420s / T420si — 11.1V Li-ion Replacement Battery (0A36287)

This 11.1V, 3600mAh (39.96Wh) Li-ion battery fits the Lenovo ThinkPad T420s and T420si business laptops. It replaces OEM part numbers including 0A36287, 42T4844, 42T4845, 42T4846, 42T4847, 45N1036, and 45N1037. The T420s uses a slim 13.10mm profile battery — confirm your existing part number before ordering.

  • T420s and T420si compatibility: Both models share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The T420si is the Intel integrated graphics variant — the battery is electrically identical across both chassis. Cross-reference against the OEM part number on your original cell to confirm fit.
  • Bench tested on actual hardware: We ran this cell on a T420s under combined CPU and display load. The BMS held the discharge curve without premature cutoff and accepted a full charge cycle without triggering the BIOS charge-fault flag.
  • BIOS learn cycle after install: After fitting this battery, run one full discharge to hibernate-cutoff, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle. Skipping it causes the health warning that appears in Lenovo Vantage or Power Manager after every cell swap — it is a calibration state, not a battery fault.

Why the T420s BIOS reports poor health immediately after a new battery install

The ThinkPad BIOS reads health data from the battery's EEPROM on first contact. A new cell ships with factory default EEPROM values that do not match Lenovo's expected charge history profile. The BIOS interprets this mismatch as a degraded cell and flags it accordingly. One full discharge-to-hibernate followed by an uninterrupted charge to 100% writes updated data and clears the warning in Lenovo Vantage and the BIOS battery status screen.

T420s shutting down at 20–30% charge shown on the fuel gauge

This is a voltage cliff — under combined CPU and display load, the cell voltage drops faster than the fuel gauge IC can track. The IC was calibrated against the old, degraded cell and its discharge curve no longer maps accurately to the new chemistry. The laptop hits the BIOS low-voltage cutoff before the displayed percentage reaches zero. Run two to three full discharge-and-charge cycles to recalibrate the fuel gauge IC against the new cell; after calibration the shutdown threshold should align with a displayed level below 5%.

Compatible Models

ThinkPad T420s ThinkPad T420si Thinkpad T420s 4171-A13

Replaces Part Numbers

0A36287 42T4844 42T4845 ASM 42T4846 42T4847 0A36309 42T4846 45N1036 45N1037

Technical Specifications

Voltage11.1V
Amp Hours3600mAh
Capacity3600mAh
Rate39.96Wh
Net Weight319.4g /11.27 oz
Gross Weight459.4g /16.20 oz
Approximate Weight459.4g /16.20 oz
Dimension 220.40 x 77.80 x 13.10 mm

Product Highlights

  • Brand: Lenovo
  • 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

Lenovo Vantage is showing the new T420s battery as "unknown" or 0% — is the cell dead on arrival?

It is not dead. The fuel gauge IC in the T420s reads the battery's EEPROM to build its state-of-charge model, and a new cell ships with factory defaults the IC does not recognise yet. Plug in the charger and leave it connected for a full uninterrupted charge to 100% — do not interrupt it. After one complete charge cycle, Vantage should resolve the status correctly.

Why does the T420s battery stop charging at exactly 80% and go no further?

This is a BIOS-controlled charge limit, not a fault with the cell. Lenovo's Power Manager and newer BIOS firmware versions include a charge threshold setting that caps charging at 80% to reduce long-term cell stress during AC-tethered use. Open Lenovo Vantage or the legacy Power Manager utility, navigate to the battery charge threshold settings, and set the stop threshold to 100%.

System information shows the wrong Wh rating for this battery — it reports a different number than the 39.96Wh on the listing. What is happening?

The Wh value shown in Windows or the BIOS is pulled from the battery's EEPROM, which stores the rated capacity written at the factory. If the figure differs from the label spec, the EEPROM value and the physical cell chemistry are reporting against slightly different reference conditions — this is a data display discrepancy, not a capacity loss. Run the battery through one full discharge-to-hibernate and a full recharge; the BIOS recalculates actual Wh from the measured cycle and the displayed figure will update to reflect real capacity.

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