About this replacement
Sugar Y12S — 3.8V Li-ion Replacement Battery (Y12S)
This 3.8V, 2300mAh Li-ion battery is a direct cell replacement for the Sugar Y12S smartphone. It fits the Y12S only — confirm your model before ordering. Capacity is rated at 8.74Wh, matching the original cell specification.
- Y12S platform fit: The Y12S uses a fixed connector pinout and a BMS handshake tied to the charge IC on the main board. This cell matches that connector layout and communicates correctly with the onboard fuel gauge so the OS receives valid capacity data from the first boot.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on a Y12S board. The BMS accepted the cell without fault flags, the charge IC stepped through CC and CV phases normally, and the fuel gauge reported state-of-charge without erratic jumps after the first full cycle.
- First-cycle fuel gauge recalibration: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate its coulomb counter against the new cell's discharge curve before high-current charging pushes into an uncalibrated state.
Why the Y12S reports wrong battery percentage after a cell swap
The Y12S fuel gauge IC stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches the new cell's actual voltage-to-capacity relationship. The OS reads the old curve and reports percentages that don't match real charge state. One full discharge-to-charge cycle — draining to auto-shutdown, then charging uninterrupted to 100% — forces the coulomb counter to rebuild its reference curve against the new cell.
Sudden shutdown at 20–30% on the replacement cell
This happens when the cell voltage drops below the modem or display load threshold before the fuel gauge reaches 0%. A fresh cell with an uncalibrated fuel gauge hits a voltage cliff under peak load — the BMS cuts output to protect the cell even though the display shows charge remaining. Run one full uninterrupted cycle and confirm the phone does not enter any battery saver mode during discharge. After recalibration, the cutoff should align closer to 3.2V under load.