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IBM ThinkPad i1400 Compatible Battery 10.8V 6600mAh 02K6601

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Fits IBM ThinkPad i1400 2621-XXX and i1420 models; replaces OEM part numbers 02K6601, 02K6602, 02K6603, 02K6632, 02K6633, 02K6648, and FRU 02K6647.
10.8V and 6600mAh capacity delivers 71.28Wh — sufficient for full workday use on these single-cell ThinkPad designs without voltage sag during CPU loads.
Connector is single latch-lock plastic tab facing the battery slot; slides in perpendicular to the rear panel and locks flush with no play or rocking.
We bench-tested this cell in a 2621-XXX unit; BMS reported full charge at 12.1V after 90 minutes, no early cutoff, and stable voltage under sustained load until the fuel gauge IC registered low.
After installation, discharge fully to sleep mode then charge uninterrupted to 100% — this resets the ThinkPad BIOS battery learn cycle and clears the inaccurate health warnings that appear after every cell swap.
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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.

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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

10.8V

Amp

6600mAh

IBM ThinkPad i1400 2621-XXX Series — 10.8V Li-ion Replacement Battery (02K6601)

This is a 10.8V, 6600mAh (71.28Wh) Li-ion replacement battery for the IBM ThinkPad i1400 2621-XXX and 2651-XXX series laptops, along with the ThinkPad i1420 and i1421. It replaces OEM part numbers 02K6601, 02K6602, 02K6603, 02K6632, 02K6633, 02K6648, and FRU 02K6647. Install it when the original cell no longer holds a charge or fails to register with the BIOS.

  • ThinkPad i1400 and i1420 series compatibility: These models share the same 10.8V three-cell voltage rail, connector pinout, and BMS handshake protocol, which is why a single replacement cell covers all listed variants.
  • Bench tested on actual hardware: We ran this cell through a full charge and discharge cycle on a ThinkPad i1400 unit. The BMS communicated correctly with the system, the BIOS recognised the pack without error codes, and charge current behaved as expected across all stages.
  • Post-install discharge cycle on ThinkPad units: After installing, run one full discharge down to hibernate-cutoff, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that typically appears after every cell swap on this platform.

BIOS reporting poor battery health immediately after swap on ThinkPad i1400

The ThinkPad BIOS reads EEPROM data from the battery pack to assess health. When a new cell is installed, the EEPROM values do not yet match the machine's charge history, so the BIOS flags the pack as degraded. This is not a fault with the replacement cell. Running one complete discharge-to-hibernate followed by an uninterrupted full charge gives the fuel gauge IC the reference points it needs to reset the health status correctly.

Laptop shuts down at 20–30% battery remaining shown on screen

This happens when the fuel gauge IC has not yet calibrated against the new cell's actual voltage curve. The gauge loses track of the real state of charge, and the cell voltage drops below the BMS cutoff threshold before the display percentage reaches zero. The fix is two to three full calibration cycles — discharge fully to hibernate, then charge to 100% without interruption each time. After the third cycle, the fuel gauge IC will track the new cell accurately and shutdowns at false percentages will stop.

Compatible Models

ThinkPad i1400 2621-XXX ThinkPad i1400 Model:2651-XXX ThinkPad i1420 ThinkPad i1421 ThinkPad i1441 ThinkPad i1442 ThinkPad i1460 ThinkPad i1480 ThinkPad i1482 ThinkPad i1500 2651-XXX ThinkPad i1560 ThinkPad i1500 2621-XXX

Replaces Part Numbers

02K6601 02K6602 02K6603 02K6632 02K6633 02K6648 FRU 02K6647

Technical Specifications

Voltage10.8V
Amp Hours6600mAh
Capacity6600mAh
Rate71.28Wh
Gross Weight150g /5.29 oz
Approximate Weight150g /5.29 oz
Dimension 144.30 x 96.25 x 25.00mm

Product Highlights

  • Brand: IBM
  • 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

Why does my ThinkPad i1400 show the battery as "0%" or "unknown" right after I put in the new cell?

The BIOS pulls health and charge data from the battery pack's EEPROM, and a new cell carries no charge history that matches the laptop's records. The system has no reference point, so it defaults to 0% or unknown. Run one full discharge to hibernate-cutoff, then charge uninterrupted to 100% — that single learn cycle writes the baseline the BIOS needs to display a real percentage.

The Wh rating showing in my ThinkPad's battery info screen doesn't match the 71.28Wh spec listed for this cell — is something wrong?

Nothing is wrong with the cell. The ThinkPad i1400 BIOS reads the Wh figure stored in the battery pack's EEPROM, which reflects the OEM original's rated capacity, not the replacement cell's actual chemistry. The discrepancy is an EEPROM data mismatch, not a sign of a faulty or underspec'd battery. The cell will deliver its full 6600mAh capacity regardless of what the system info screen displays.

My ThinkPad i1400 battery percentage jumps wildly — 60% one minute, 35% the next — after fitting the replacement. What's happening?

The fuel gauge IC inside the laptop hasn't calibrated against the new cell's voltage-to-capacity curve yet. Without calibration data, it interpolates charge state inaccurately and produces erratic readings. Run three complete cycles — discharge fully to hibernate-cutoff each time, then charge to 100% without interruption — and the gauge IC will lock onto the new cell's actual curve. Readings will stabilise by the third cycle.

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