About this replacement
Lenovo ThinkPad E120 Series — 11.1V Li-ion Replacement Battery (0A36290)
This 11.1V, 4400mAh (48.84Wh) Li-ion battery replaces the original cell in the Lenovo ThinkPad E120 and ThinkPad Edge E120 series notebooks. It covers OEM part numbers including 0A36290, 42T4943, 45N1058, and related variants. Install it when the original cell no longer holds sufficient charge for portable use.
- ThinkPad E120 and Edge E120 compatibility: These models share the same 11.1V three-cell architecture, connector pinout, and BMS handshake protocol — meaning one cell covers the full variant range including the 30434NC, 30434SC, and 30434TC chassis without modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a ThinkPad E120 unit. The BMS negotiated correctly with the EC, charge current tapered normally at the top of the curve, and the protection circuit tripped cleanly at the low-voltage threshold.
- Post-install discharge cycle: After fitting this cell, run one full discharge to hibernate 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 on this platform.
BIOS reporting poor battery health immediately after fitting a new cell
The ThinkPad EC reads health data from the battery's EEPROM and compares it against stored charge history from the previous cell. A brand-new cell has no accumulated cycle data, so the EC flags it as degraded — this is a data mismatch, not a fault with the replacement. Running the BIOS battery learn cycle writes fresh baseline data from the new cell. After one full discharge-to-hibernate and an uninterrupted charge to 100%, the health indicator updates and the warning clears.
Laptop shuts down abruptly at 20–30% charge shown on screen
This happens when the fuel gauge IC has not yet calibrated against the new cell's actual discharge curve. The gauge loses accuracy under combined CPU and display load — voltage drops faster than the IC predicts, and the protection circuit cuts power before the displayed percentage reaches zero. It is not a faulty cell. Run two to three full discharge-to-hibernate cycles to let the IC map the real capacity curve. After calibration, the cutoff point will align with the displayed percentage at or below 5%.