Lenovo ThinkPad E40 Compatible Battery 11.1V 42T4235
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Lenovo ThinkPad E40 Compatible Battery 11.1V 42T4235 - 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.
Lenovo ThinkPad E40 Compatible Battery 11.1V 42T4235 - is backordered and will ship as soon as it is back in stock.
Voltage
11.1V
Amp
6600mAh
Lenovo ThinkPad E40 / E50 Series — 11.1V Li-ion Replacement Battery (42T4235)
This is an 11.1V, 6600mAh (73.26Wh) Li-ion battery for the Lenovo ThinkPad E40, E50, and ThinkPad Edge 14" family. It cross-references over 80 OEM part numbers including 42T4731, 42T4757, 45N1000, and 0A36303. The connector, BMS handshake protocol, and cell count all match the original Lenovo specification for these platforms.
- ThinkPad E40 / E50 platform fit: These models share a common 6-cell Li-ion architecture, identical connector pinout, and the same BMS communication line used by the ThinkPad EC firmware. One battery covers the full E40, E50, and ThinkPad Edge 0578 series because Lenovo kept the power subsystem consistent across that generation.
- Bench tested on actual hardware: We cycled this cell on a ThinkPad E40 and monitored BMS communication through the EC. The protection circuit responded correctly to charge termination, cell balancing, and over-discharge cutoff at the expected low-voltage threshold — no false fault flags during the test run.
- Post-install calibration on ThinkPad EC: After fitting this battery, run one full discharge to hibernate cutoff, then charge uninterrupted to 100%. This forces the ThinkPad EC to complete a battery learn cycle against the new cell data and clears the inaccurate health warning that appears after any cell swap.
Why the ThinkPad E40 BIOS reports poor battery health after a new cell install
The ThinkPad EC stores learned charge data from the previous cell in EEPROM. When a new battery arrives, that stored data no longer matches the actual cell chemistry, so the EC flags it as degraded. This is an EEPROM mismatch, not a fault with the replacement cell itself. Running one full discharge-to-hibernate followed by an uninterrupted charge to 100% overwrites the old learn data. After one or two full cycles, the health indicator corrects itself.
ThinkPad E40 shutting down abruptly at 20–30% charge shown
This happens when the fuel gauge IC has not yet calibrated against the new cell's actual voltage curve. The displayed percentage stays optimistic until the cell voltage drops sharply under combined CPU and display load — at that point the EC triggers an emergency cutoff before the gauge catches up. The fix is to complete two or three full discharge-to-recharge cycles so the fuel gauge IC maps the real voltage-to-capacity curve. Once calibrated, the system will begin stepping down load and warning correctly before the cell reaches its 2.5V per-cell cutoff floor.
Compatible Models
Replaces Part Numbers
Technical Specifications
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
My ThinkPad E40 shows the battery as "Unknown" or 0% right after installing this replacement — is the cell dead?
The cell is not dead. The ThinkPad EC reads identity and capacity data from the battery's EEPROM, and when that data doesn't match what it learned from the old pack, it reports "Unknown" or refuses to display a percentage. Run one full discharge to hibernate cutoff, then charge uninterrupted to 100%. That single learn cycle is usually enough for the EC to accept the new cell and display a correct state of charge.
The Wh rating shown in Lenovo Vantage or Device Manager doesn't match what's printed on the battery label — which one is right?
The figure in software is pulled from the battery's EEPROM, which stores the OEM-rated value from when that firmware was written — it does not update dynamically to reflect the replacement cell's actual rated capacity. The physical label and the product data (73.26Wh at 11.1V, 6600mAh) are the authoritative figures for this cell. The software discrepancy is an EEPROM reporting difference, not a capacity shortfall — no action needed beyond completing the battery learn cycle.
Charge stops at around 80% and won't go higher — is the battery faulty or is something limiting it?
Lenovo's BIOS includes a charge threshold feature, sometimes called "Battery Conservation Mode" in Lenovo Vantage or the Power Manager settings. When enabled, it deliberately caps charging at 80% to reduce cell stress over time. Open Lenovo Vantage, go to Power, and check the charge threshold settings — switching to "Full Charge" mode allows the battery to reach 100%. This is a firmware-controlled limit, not a fault with the replacement cell.
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