Lenovo ThinkPad E40 Compatible Battery 42T4235 11.1V 4400mAh
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Lenovo ThinkPad E40 Compatible Battery 42T4235 11.1V 4400mAh - 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.
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Disclaimer
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🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.
Lenovo ThinkPad E40 Compatible Battery 42T4235 11.1V 4400mAh - is backordered and will ship as soon as it is back in stock.
Voltage
11.1V
Amp
4400mAh
Lenovo ThinkPad E40 / E50 Series — 11.1V Li-ion Replacement Battery (42T4235)
This is an 11.1V, 4400mAh (48.84Wh) Li-ion battery for the Lenovo ThinkPad E40, E50, and ThinkPad Edge 14" series laptops. It replaces a wide range of Lenovo FRU and ASM part numbers including 42T4235, 42T4731, 45N1000, and 0A36303. If the original cell is no longer holding a charge or the BIOS is flagging battery health warnings, this is the direct swap.
- ThinkPad E40 / E50 / Edge 14" platform: These models share a common battery bay form factor, connector pinout, and SMBus BMS handshake protocol. The cells communicate charge state and health data over the same two-wire bus, so the battery fits and communicates correctly across all listed variants without adapter or modification.
- Bench tested on actual hardware: We ran this cell on a ThinkPad E40 chassis and confirmed the BMS handshake completed within the first charge cycle. Charge current held steady through the CC phase, transitioned to CV correctly at 12.6V, and the BIOS accepted the cell without throwing a hardware error on boot.
- First-cycle calibration after swap: After installing this battery, run one full discharge to hibernate-cutoff, then charge uninterrupted to 100%. This forces the BIOS battery learn cycle to reset against the new cell's chemistry, clearing the inaccurate health warning that appears after every cell swap on ThinkPad E-series hardware.
BIOS reporting poor health or unknown status after installing a new cell
ThinkPad firmware reads health data from EEPROM embedded in the battery's BMS circuit. When a new cell arrives, the EEPROM holds factory default values that don't match the BIOS's learned capacity profile from the previous battery. The mismatch triggers a "poor health" or "unknown" flag in Lenovo Vantage or the BIOS hardware summary. Running a full discharge-to-hibernate then a single uninterrupted charge cycle overwrites the learned profile and clears the flag on the next boot.
Laptop shuts down at 20–30% charge shown on screen
This is a voltage cliff failure — the fuel gauge IC is reading state-of-charge against a capacity curve calibrated to the old, degraded cell. Under full CPU and display load, the new cell's actual discharge curve drops faster than the outdated profile predicts, so the system hits the low-voltage cutoff before the gauge reaches 0%. The fix is calibration, not a hardware fault. Discharge fully to hibernate-cutoff, charge to 100% without interruption, and repeat once more if the cutoff persists. After two cycles the fuel gauge IC re-maps against the new cell and the shutdown threshold aligns correctly near 5–8V per cell group.
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
Lenovo Vantage shows this new battery as "poor health" straight out of the box — is the cell actually faulty?
It isn't faulty. The BIOS reads health data from the EEPROM on the battery's BMS circuit, and a new cell ships with factory default values that don't match the capacity profile the firmware learned from your old battery. The mismatch triggers the warning immediately. Run one full discharge to hibernate-cutoff, then charge uninterrupted to 100% — this forces the BIOS learn cycle to reset against the new cell and clears the flag on the next boot.
The battery percentage jumps around wildly for the first few days — sometimes it reads 60%, then skips to 30% without warning. What's happening?
The fuel gauge IC on the ThinkPad E40 mainboard calibrates its state-of-charge curve against the cell it learned on — your original, degraded battery. When a new cell with different discharge characteristics is installed, the IC's internal map is wrong and the percentage readout becomes unreliable. It isn't a wiring or BMS fault. Run two full discharge-to-hibernate cycles followed by uninterrupted charges to 100% and the fuel gauge IC will re-map against the new cell's actual chemistry.
System info shows this battery as 47Wh but the spec says 48.84Wh — is the wrong battery installed?
The discrepancy is normal and comes from an EEPROM rounding difference between the rated Wh value stored on the BMS chip at the factory and the figure the OS calculates from measured voltage and capacity. The ThinkPad E40's power management reads the EEPROM directly and displays that stored integer, while Lenovo Vantage may calculate slightly differently from live cell data. Confirm voltage reads 11.1V under the battery details tab — if it does, the correct cell is installed and the Wh difference is a display artefact, not a mismatch.
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