About this replacement
Lenovo Yoga 900S-12ISK — 7.4V Li-Polymer Replacement Battery (L15M4P20)
This is a 7.4V 6900mAh (51.06Wh) Li-Polymer replacement battery for the Lenovo Yoga 900S-12ISK ultrabook. It fits the Yoga 900S 12ISK, Yoga 4S, and the 80ML001WGE variant. It replaces OEM part numbers L15M4P20, L15L4P20, 5B10J50660, 5B10J50662, and 5B10J66116.
- Yoga 900S-12ISK platform fit: All Yoga 900S-12ISK variants share the same 7.4V battery bay, connector pinout, and BMS handshake protocol. The slim 3.35mm cell profile is specific to this chassis — a thicker cell will not seat correctly under the keyboard deck.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Yoga 900S-12ISK unit. The BMS handshake completed correctly, the fuel gauge IC registered the new cell, and charge current stepped down at the expected 80% and 95% thresholds without fault codes.
- Post-install calibration on the Yoga 900S: After fitting this battery, run one full discharge to hibernate-cutoff, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning the firmware throws after every cell swap. Skipping this step leaves the fuel gauge IC reading against the old cell's EEPROM data.
Why the Yoga 900S-12ISK BIOS reports poor battery health after a cell swap
The Yoga 900S-12ISK stores battery health data in EEPROM on the battery's protection circuit. When a new cell is installed, the BIOS reads stale EEPROM metrics from the previous cycle history and flags the battery as degraded. This is a firmware behaviour, not a fault with the replacement cell. Running the BIOS battery learn cycle — one full discharge to cutoff followed by a full uninterrupted charge — rewrites the stored data against the new cell's actual capacity. After one or two calibration cycles, the health indicator returns to normal.
Yoga 900S-12ISK shutting down at 20–30% charge shown
This happens when the cell voltage drops sharply under the combined load of the CPU, display, and storage — a voltage cliff that the fuel gauge IC did not predict. The gauge was calibrated against the old cell's discharge curve, so the percentage shown does not match actual remaining capacity. It is not a fault in the replacement cell. Run a full discharge-to-hibernate cycle and charge to 100% without interruption — after two cycles the gauge recalibrates to the new cell's curve and the early shutdowns stop.