About this replacement
Lenovo IdeaPad S41 Series — 7.4V Li-Polymer Replacement Battery (L14L2P21)
This 7.4V, 4050mAh (29.97Wh) lithium-polymer cell replaces the OEM battery in the Lenovo IdeaPad S41 family, including the S41-70, S41-70AM, and S41-70-ISE. It matches the original slim 6.20mm profile so it fits inside the chassis without modification. Part numbers L14L2P21 and L14M2P21 both cross-reference to this cell.
- S41 series compatibility: The S41, S41-70, S41-70AM, and related variants all share the same 7.4V two-cell Li-Polymer architecture, the same 10-pin connector, and the same BMS handshake. One cell covers the full line because Lenovo used an identical power rail and protection circuit across every S41 SKU.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on an S41-70 unit. The BMS communicated charge state correctly, protection tripped at the expected low-voltage threshold, and the fuel gauge IC registered the cell without error flags.
- Post-install calibration on the S41: After fitting this cell, run one full discharge until the laptop hibernates, then charge uninterrupted to 100% without interruption. This gives the S41's fuel gauge IC a clean baseline against the new cell chemistry and clears the inaccurate health warning that often appears after every cell swap.
Why the S41 BIOS reports poor battery health immediately after a cell swap
The S41 stores learned capacity data in EEPROM on the battery's protection circuit board. When a new cell goes in, the BIOS compares current readings against the stored profile from the old, degraded cell and flags a mismatch as poor health. This is not a fault with the replacement cell. Running one full discharge-to-hibernate cycle followed by an uninterrupted charge to 100% resets the learn cycle. After two to three full cycles, the BIOS health indicator updates to reflect the new cell's actual capacity.
S41 shutting down at 20–30% charge shown on screen
This happens when the fuel gauge IC is still calibrated to the old cell's voltage curve. Under full CPU and display load, the new cell's actual voltage drops faster than the miscalibrated gauge predicts, hitting the BMS low-voltage cutoff before the percentage reaches zero. It looks like a sudden shutdown, but the cell is simply at a lower real voltage than the gauge shows. The fix is a full discharge calibration cycle — let the laptop run down to hibernate cutoff, then charge uninterrupted to 100%. After one to two full cycles, the gauge re-maps to the new cell and shutdown-at-percentage behaviour stops.