About this replacement
Lenovo IdeaPad S300 / S400 Series — 14.8V Li-ion Replacement Battery (L12S4Z01)
This is a 14.8V, 2200mAh Li-ion replacement battery for the Lenovo IdeaPad S300, S400, S405, and related S-series notebooks. It replaces OEM parts L12S4Z01, L12S4L01, and 4ICR17/65. Install it when the original cell no longer holds adequate charge or fails to power the laptop away from AC.
- IdeaPad S300 / S400 / S405 compatibility: These models share the same 14.8V four-cell Li-ion architecture, connector pinout, and BMS communication protocol — which is why one cell SKU covers the entire range. The BMS handshake uses the same EEPROM data structure across all three platforms.
- Bench tested on actual hardware: We ran this cell on an IdeaPad S400 and monitored charge acceptance through a full CC/CV cycle. The BMS negotiated correctly, charge tapered at 16.8V as expected, and no protection flags tripped during load testing at full CPU and display draw.
- BIOS learn cycle after install: After fitting this battery, run the laptop down to hibernate cutoff — do not force-shutdown — then charge uninterrupted to 100%. This one full discharge-to-charge cycle resets the BIOS battery learn cycle and clears the inaccurate health or capacity warning that appears after every cell swap on IdeaPad S-series units.
Why the IdeaPad S300 shuts down at 20–30% remaining after a battery swap
The IdeaPad S-series fuel gauge IC calibrates its empty-tank threshold against the original cell's discharge curve stored in EEPROM. A new cell has a slightly different voltage-versus-capacity curve, so the gauge reads the remaining charge incorrectly. Under combined CPU and display load, the actual cell voltage drops faster than the gauge expects, and the system hits its low-voltage cutoff while the OS still shows 20–30%. Running two or three full discharge-to-100% charge cycles recalibrates the fuel gauge IC against the new cell's actual curve and corrects the early shutdown behaviour.
BIOS reporting battery health as "poor" or "replace" immediately after install
Lenovo's BIOS reads health status from EEPROM data written by the original cell — not from live voltage measurements. When a new cell is installed, the EEPROM cycle count and wear flags from the old battery still sit in firmware memory, triggering the warning. This is not a fault with the replacement cell. Run the battery learn cycle: discharge fully to hibernate, then charge to 100% without interruption. After one complete cycle, the BIOS resets its health register and the warning clears.