About this replacement
Lenovo IdeaPad Z400 / Z500 Series — 14.8V Li-ion Replacement Battery (L12S4K01)
This is a 14.8V 2200mAh (32.56Wh) Li-ion replacement battery for the Lenovo IdeaPad Z400, Z400A, Z500, and Z500A series notebooks. It replaces OEM part numbers L12S4K01, L12S4E21, L12L4K01, L12M4E21, L12M4K01, and L12M4F02. The connector and cell configuration match the original 4-cell pack exactly.
- Z400 and Z500 platform compatibility: Both series run the same 14.8V four-cell architecture with an identical BMS handshake protocol. The battery management controller on this pack communicates with the Lenovo EC firmware on both chassis without modification.
- Bench tested on actual hardware: We ran this cell on an IdeaPad Z500 under sustained CPU and display load. The BMS held voltage above the 12V cutoff threshold through full discharge, and charge termination triggered correctly at capacity without false-positive fault flags.
- Post-install discharge cycle on Lenovo IdeaPad: After fitting 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 and clears the inaccurate health warning that appears after every cell swap.
Why the IdeaPad Z400 shuts down at 20–30% after a battery swap
The IdeaPad EC reads voltage curves stored from the old cell to estimate remaining capacity. A new cell with different internal resistance produces a steeper voltage drop under full CPU plus display load than the stored curve predicts. The EC interprets this as a critical low-voltage event and triggers an immediate shutdown even though the gauge shows 20–30% remaining. Running two to three full discharge and charge cycles lets the fuel gauge IC recalibrate its curve against the new cell's actual impedance, and the false shutdowns stop.
BIOS reporting battery health as poor or unknown immediately after fitting a new cell
The BIOS reads health data from the EEPROM on the old battery pack, not from live cell measurements. When a new pack is installed, the EEPROM presents factory-default values that the Lenovo firmware flags as mismatched or degraded against its stored baseline. This is not a fault with the replacement cell. Enter the Lenovo BIOS power settings, disable and re-enable battery care mode if active, then run the battery learn cycle — the health status normalises once the EC has logged one complete charge and discharge profile from the new cell.