About this replacement
Lenovo ThinkPad X1 Yoga 2018 — 15.36V Li-Polymer Replacement Battery (L17C4P71)
This is a 15.36V, 3500mAh (53.76Wh) Li-Polymer battery for the Lenovo ThinkPad X1 Yoga 2018 2-in-1 convertible laptop. It replaces OEM part numbers L17C4P71, L17M4P71, SB10K97623, SB10K97624, and several others used across the 2018 X1 Yoga lineup. Fits 20LD-series variants including 20LD000KCD, 20LD000SCD, and 20LD000TCD.
- 20LD-series compatibility: All 2018 X1 Yoga 20LD variants share the same 15.36V four-cell Li-Polymer pack, connector pinout, and BMS handshake protocol — which is why multiple OEM part numbers cross-reference to a single physical cell configuration.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the ThinkPad platform. The BMS negotiated correctly with the EC firmware, reported state-of-charge without error flags, and held stable voltage through simulated CPU and display load.
- First-cycle calibration on X1 Yoga: After fitting, run the laptop down to hibernate cutoff on battery power alone, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning the EC logs after every cell swap.
Why the X1 Yoga 2018 BIOS reports poor battery health after a cell swap
The ThinkPad embedded controller reads cycle count, charge history, and health data stored in the old cell's EEPROM. A new cell arrives with a blank or mismatched EEPROM, so the EC immediately flags it as degraded. This is a firmware classification issue, not a fault with the replacement cell. Running one full discharge-to-hibernate followed by an uninterrupted full charge gives the EC enough data to overwrite that flag and re-establish an accurate health baseline.
Laptop shuts down at 20–30% charge shown after battery replacement
The fuel gauge IC in the new cell hasn't yet calibrated its voltage-to-capacity curve against your specific usage load. Under combined CPU and display draw, the cell voltage drops faster than the uncalibrated gauge predicts, and the EC triggers a protective shutdown before the displayed percentage reaches zero. This is not a faulty cell — it corrects itself over two to three full charge and discharge cycles. After calibration, the gauge stabilises and shutdowns stop occurring above 10–12% shown.