About this replacement
Lenovo ThinkPad Edge E550 / E555 Series — 10.8V Li-ion Replacement Battery (45N1758)
This is a 10.8V, 4400mAh (47.52Wh) Li-ion replacement battery for the Lenovo ThinkPad Edge E550, E550C, and E555 series notebooks. It installs directly in place of the original pack and connects via the standard ThinkPad multi-pin power and data connector. Compatible OEM part numbers include 45N1758, 45N1759, 45N1760, 45N1761, 45N1763, and 4X50G59217, among others.
- E550 / E550C / E555 platform fit: These models share the same 10.8V battery rail, identical connector pinout, and the same BMS handshake protocol across the E5xx generation — one cell fits the entire lineup regardless of minor SKU suffix differences.
- Bench tested on actual hardware: We ran this cell on an E550 unit under combined CPU and display load. The BMS held voltage above the 10.0V cutoff threshold throughout the discharge cycle and reported charge state correctly to the EC controller.
- Post-install calibration on the E550: After fitting this battery, run one full discharge to the hibernate-cutoff point, 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 ThinkPad hardware.
BIOS reporting poor battery health immediately after fitting a new cell
The ThinkPad EC reads learned capacity data stored in the old cell's EEPROM. When a new cell goes in, that learned data is gone and the EC flags the battery as degraded before it has run a single cycle. This is not a fault with the replacement cell — it is the EC comparing zero learned cycles against its own threshold. Run one full discharge-to-hibernate then a full uninterrupted charge. After two to three cycles the EC recalibrates and the health warning clears.
Laptop shuts off at 20–30% charge shown on screen
The fuel gauge IC on the E550 motherboard maps voltage curves from the previous cell. A fresh cell has a slightly different voltage-to-capacity slope, so the gauge reads 20–30% while the actual cell voltage is already near the low-cutoff cliff. Under full CPU plus display load, the voltage drops sharply and the EC triggers an emergency shutdown. Force a full discharge to hibernate, charge to 100% without interruption, and repeat twice. After recalibration the gauge tracks the new cell's curve accurately and the cutoff moves back to the correct threshold near 3.0V per cell.