IBM ThinkPad T61 Replacement Battery 10.8V 6600mAh ASM 42T5265
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IBM ThinkPad T61 Replacement Battery 10.8V 6600mAh ASM 42T5265 - 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.
IBM ThinkPad T61 Replacement Battery 10.8V 6600mAh ASM 42T5265 - is backordered and will ship as soon as it is back in stock.
Voltage
10.8V
Amp
6600mAh
IBM ThinkPad T61 7659 Series — 10.8V Li-ion Replacement Battery (ASM 42T5265)
This 10.8V, 6600mAh Li-ion battery replaces the original pack on the IBM ThinkPad T61 7659 and compatible models including the ThinkPad T400 2764, T61 6480, and R400. It slots into the standard ThinkPad battery bay and connects via the same multi-pin bus used by the OEM pack. Capacity matches the original 71.28Wh specification.
- T61 and T400 platform compatibility: These models share IBM's 10.8V three-cell-in-series architecture, the same 9-pin SMBus connector, and an identical BMS handshake protocol — which is why one cell works across the T61, T400, and R400 lines without firmware changes.
- Bench tested on actual hardware: We ran this cell on a T61 7659 mainboard and confirmed the SMBus communication initialised correctly, BIOS recognised the pack without error flags, and the BMS held charge termination at the correct voltage ceiling.
- First-cycle calibration on the T61: After installing, discharge the laptop normally to the hibernate cutoff, then charge uninterrupted to 100% without interruption. This forces the ThinkPad's fuel gauge IC to re-learn the new cell's actual capacity curve and clears the inaccurate health warning that appears in Lenovo Power Manager after every cell swap.
BIOS reporting poor battery health immediately after fitting a new cell
The ThinkPad BIOS reads health data from the battery's EEPROM — not from a live measurement. When a new cell arrives, that EEPROM contains factory defaults that don't match the system's learned charge history, so the BIOS flags it as degraded. Running a full discharge-to-hibernate followed by an uninterrupted charge resets the learn cycle. After two to three full cycles, the BIOS health reading aligns with the actual cell condition. No firmware update or BIOS reset is required — calibration cycles fix this.
Laptop shuts down abruptly at 20–30% charge shown on screen
This happens when the cell can no longer sustain the voltage rail under combined CPU and display load — the voltage drops off a cliff faster than the fuel gauge IC can track it. The OS gauge shows 20–30% remaining because it's reading a state-of-charge estimate, not live voltage under load. A depleted original cell hits this cliff early; a fresh cell pushes that point much closer to true empty. If a new cell still cuts out above 15%, recheck the battery contacts on the mainboard connector for oxidation and confirm the hibernate threshold in Power Manager is set no higher than 5%.
Compatible Models
Replaces Part Numbers
Technical Specifications
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
My ThinkPad T61 shows the battery as "unknown" with 0% in the OS right after fitting the new cell — what's wrong?
The fuel gauge IC on the T61 mainboard lost its reference data when the old cell was removed, and the new cell's EEPROM hasn't synced with it yet. This is an EEPROM initialisation gap, not a faulty battery. Run one full discharge to the automatic hibernate cutoff, then charge uninterrupted to 100%. After that first complete cycle the OS will read the correct state-of-charge.
The battery charge indicator jumps around wildly — showing 60%, then 45%, then 70% within minutes. Is the cell defective?
The fuel gauge IC needs several full charge-discharge cycles to build an accurate model of the new cell's capacity curve. Until it does, the state-of-charge estimate swings between reference points left over from the old cell. We see this on the bench for the first two to three cycles with every replacement cell on this platform. Run two full discharge-to-hibernate and full recharge cycles back-to-back and the gauge will stabilise.
Why does Windows report this battery as 58Wh when the spec says 71.28Wh?
Windows reads the rated design capacity stored in the cell's EEPROM and divides it by a wear factor the mainboard has accumulated from the old pack's charge history. After the T61's battery learn cycle completes — one full discharge to hibernate, one uninterrupted charge to 100% — the reported Wh figure updates to reflect the actual new cell data. If it still reads low after three cycles, open Lenovo Power Manager and check whether a charge threshold is set below 100%, which reduces the reported usable capacity proportionally.
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