About this replacement
Lenovo S660 / S668T — 3.8V Li-Polymer Replacement Battery (BL222)
This is a 3.8V, 3000mAh (11.4Wh) lithium-polymer cell that replaces the OEM BL222 battery in the Lenovo S660 and S668T smartphones. It fits both model variants and restores power capacity when the original cell has degraded or failed. Install requires removing the back cover and disconnecting the flex connector — no soldering.
- S660 and S668T compatibility: Both handsets share the same battery bay dimensions, flex connector pinout, and BMS handshake protocol, which is why a single BL222 cell covers both. The 76.26 × 59.73 × 5.11 mm footprint seats flush in either chassis without modification.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on the S660 platform. The BMS communicated correctly with the charge IC, accepted current without tripping protection, and held stable voltage through load transitions from screen-on to modem burst.
- Fuel gauge recalibration on first cycle: Disable fast charging for the first complete discharge-charge cycle after installation. The S660's fuel gauge IC was calibrated to the old cell's discharge curve. Running one slow cycle at standard current lets it re-map against the new cell before high-current charging is applied to an uncalibrated state.
Sudden shutdown at 20–30% on the S660 after a cell swap
This is a voltage cliff issue, not a capacity fault. The Lenovo S660's power management IC monitors cell voltage in real time. A new cell with an uncalibrated fuel gauge IC can report 25% remaining while actual cell voltage drops below the shutdown threshold under modem or display load. The system interprets that voltage drop as a fault and cuts power instantly. One full slow-charge cycle lets the coulomb counter re-anchor its percentage estimates to the actual discharge curve of the new cell, which eliminates the premature cutoff.
Phone not powering on after the BL222 sat in storage
Lithium-polymer cells in storage self-discharge over time. If the BL222 dropped below approximately 2.5V per cell before installation, the BMS enters a lockout state and will not accept a normal charge current. Connect the phone to a wall charger — not a USB port — and leave it for 20 to 30 minutes without attempting to power it on. The charge IC delivers a low trickle current that slowly walks the cell voltage back above the BMS recovery threshold. Once voltage crosses roughly 3.0V, the BMS unlocks and normal charging resumes.