About this replacement
Lenovo IdeaPad K4350 Series — 14.8V Li-ion Replacement Battery (L12S4Y51)
This is a 14.8V, 2200mAh (32.56Wh) Li-ion replacement battery for the Lenovo IdeaPad K4350, K4350A, K2450, and M490S, among other compatible IdeaPad models. It fits the original L12S4Y51 and L12S4Z51 OEM part numbers. Install it when the original cell no longer holds adequate charge for portable use.
- IdeaPad K4350 and K2450 battery compatibility: These models share the same 14.8V four-cell battery architecture, connector pinout, and BMS handshake protocol — that is why one cell covers the full compatibility list. The battery management circuit communicates state-of-charge data over the same SMBus line across all listed variants.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on IdeaPad hardware, confirming the BMS handshake initialised correctly, charge termination triggered at the expected voltage ceiling, and protection cutoffs fired at the correct low-voltage threshold.
- First-cycle recalibration on the IdeaPad platform: After fitting this cell, run one full discharge until the laptop hibernates, then charge uninterrupted to 100%. This forces the BIOS battery learn cycle to reset against the new cell's actual capacity and clears the inaccurate health warning that appears after every cell swap on Lenovo IdeaPad firmware.
Why the IdeaPad K4350 shuts down at 20–30% charge remaining
This happens when the cell cannot sustain voltage under combined CPU and display load — the fuel gauge shows 25% but the cell voltage drops below the BMS cutoff threshold the moment load spikes. On a degraded original cell, this is a capacity cliff caused by aged chemistry. On a new replacement, it usually means the BIOS fuel gauge IC has not yet calibrated against the new cell's discharge curve. Run two full discharge-to-hibernate and full-charge cycles. After calibration, the reported percentage and actual cutoff will align.
BIOS reporting battery health as poor immediately after fitting a new cell
Lenovo's BIOS reads health data from EEPROM registers embedded in the battery pack — it does not measure the physical cell directly on first boot. When a new cell is installed, the EEPROM values do not match the residual learn data the BIOS stored from the old pack, so the system flags the battery as unknown or degraded. This is a data mismatch, not a faulty battery. Run the full discharge-to-hibernate then uninterrupted charge-to-100% cycle, and the BIOS will rewrite its stored health baseline against the new cell's EEPROM data.