About this replacement
Lenovo ThinkPad Yoga S1 12.5" — 14.8V Li-Polymer Replacement Battery (45N1704)
This is a 14.8V, 3150mAh Li-Polymer battery pack for the Lenovo ThinkPad Yoga S1 12.5" and Yoga 12 series ultrabooks. It replaces OEM part numbers 45N1704, 45N1705, 45N1706, and 45N1707. It fits slim-chassis convertible models including 20CDS00700 and 20CDS00800 configurations.
- ThinkPad Yoga S1 and Yoga 12 compatibility: These models share the same 14.8V internal power rail, connector pinout, and BMS handshake protocol across the 45N170x part number range. The four OEM part numbers differ by region and minor PCB revision but are electrically interchangeable within this chassis.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a ThinkPad Yoga S1 unit. The BMS communicated correctly with the system board, and the charge controller accepted the cell without flagging a hardware error.
- Post-install calibration on Lenovo convertibles: After fitting, run the laptop down to hibernate cutoff under normal use, 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 this platform.
BIOS reporting poor battery health immediately after fitting a new cell
The ThinkPad BIOS reads health status from EEPROM data embedded in the battery pack. A new cell carries factory EEPROM values that don't yet match the host system's charge history, so the BIOS flags it as degraded before any cycles have run. This is a calibration state, not a fault. One full discharge-to-hibernate followed by an uninterrupted charge to 100% resets the learn cycle. After two to three cycles, the reported health figure normalises.
ThinkPad Yoga S1 shutting down at 20–30% shown on the fuel gauge
This happens because the fuel gauge IC is still calibrated to the old cell's voltage-to-capacity curve. The new cell hits a voltage cliff under combined CPU and display load at a point the gauge still interprets as 20–30% remaining. The system board triggers shutdown before the gauge catches up. Run two full discharge-to-hibernate cycles without interruption, and the fuel gauge IC recalibrates to the new cell's actual discharge curve. If the shutdowns persist past three cycles, check the BIOS power settings and confirm the charge threshold is not capped — navigate to ThinkPad Setup → Config → Power → Disable Battery Charge Threshold.