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Wiko Lenny 4 / Harry / Robby — 3.8V Li-ion Replacement Battery (3913)

This is a 3.8V, 2400mAh Li-ion cell built to OEM part number 3913. It fits the Wiko Lenny 4, Lenny 4 Plus, Harry, and Robby smartphones. Swap it in when your original cell no longer holds a charge or causes unexpected shutdowns.

• Lenny 4 / Harry / Robby platform fit: These four models share the same battery bay dimensions, connector pinout, and BMS handshake profile — all verified against part number 3913. The cell measures 77.00 × 60.00 × 4.20mm, matching the factory slot without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the Lenny 4 platform. The BMS communicated correctly with the charge IC, accepted a full charge cycle, and held voltage within spec under sustained screen and modem load.
• First-cycle fuel gauge recalibration: After installation, disable fast charging and complete one full discharge-to-charge cycle at standard rate. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging begins.

Why the Lenny 4 reports wrong battery percentage after a cell swap

The Lenny 4 uses a fuel gauge IC that stores a learned discharge curve from the previous cell. When you install a new cell, the IC is still referencing that old curve, so reported percentage drifts from actual charge state. This mismatch is most visible between 80% and 40%, where the old curve and new cell diverge most. One complete discharge-charge cycle at standard rate forces the IC to rewrite its reference model against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops below the modem's minimum supply threshold under peak load — typically during a call, data burst, or screen-on navigation. The fuel gauge still shows 20–30% because it's reading average voltage, not instantaneous voltage under draw. A fresh cell with an uncalibrated fuel gauge IC is most vulnerable to this in the first few cycles. After two full discharge-charge cycles, the IC tightens its voltage floor estimate and the early cutoffs stop.