Wiko SAS Replacement Battery 3.85V 2700mAh LT25H426271W

Wiko SAS / U307AS — 3.85V Li-Polymer Replacement Battery (LT25H426271W)

This 3.85V, 2700mAh (10.4Wh) Li-Polymer cell replaces the original battery in the Wiko SAS and U307AS Android smartphones. It uses OEM part number LT25H426271W and matches the original cell's dimensions at 70.90 × 62.20 × 4.60mm. Install it when the original cell no longer holds charge or causes unexpected shutdowns.

• SAS and U307AS compatibility: Both models share the same battery bay geometry, connector pinout, and BMS handshake protocol, which is why a single cell covers both. The fuel gauge IC on each device reads the same voltage curve from this Li-Polymer cell without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the SAS platform. The BMS accepted the cell without a protection trip, and the charge IC stepped through trickle, constant-current, and constant-voltage phases as expected.
• First-cycle fuel gauge reset: On first use after installation, disable fast charging and run one full discharge-to-charge cycle. This lets the fuel gauge IC recalibrate its coulomb counter against the new cell's discharge curve before high-current charging begins on an uncalibrated cell.

Sudden shutdown at 20–30% on the Wiko SAS after a cell swap

A fresh Li-Polymer cell has a slightly different internal resistance profile than the aged cell the fuel gauge IC was calibrated to. Under peak load — mobile data, screen-on, or GPS active simultaneously — the new cell's voltage can dip below the BMS cutoff threshold even when the OS reports 20–30% remaining. The OS percentage is not reading actual cell voltage at that instant; it is reading a fuel gauge estimate still mapped to the old cell curve. One full discharge-charge cycle with fast charging disabled corrects the coulomb counter and eliminates premature cutoffs.

USB fast charging not working on the first cycle after replacement

On the first charge after a battery swap, the charge IC may not negotiate the fast-charge handshake with the new cell's BMS. This is a one-cycle behaviour — the BMS needs to complete one full slow charge to register the cell as authorised before it allows elevated current. Plug in via the original cable and let the phone charge fully at standard rate. Fast charging typically resumes normally on the second charge cycle without any further action.