Sugar C13 Replacement Battery 3.85V 3900mAh Li-Polymer

Sugar C13 — 3.85V Li-Polymer Replacement Battery

This is a 3.85V, 3900mAh lithium-polymer replacement battery for the Sugar C13 smartphone. It fits directly in place of the original cell when the factory battery can no longer hold a usable charge. Capacity is 3900mAh (15.02Wh) — taken from the product specification, not estimated.

• Sugar C13 fit: The C13 uses a fixed-connector Li-Polymer cell tied to the phone's fuel gauge IC. The replacement cell matches the original's physical dimensions (80.20 × 63.65 × 4.54mm) and voltage rail, so the BMS handshake completes on first boot without triggering a connector mismatch flag.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the bench. The BMS held a stable cutoff at both ends — no premature high-voltage cutoff on charge, no undervoltage lockout tripping at rest. Coulomb counter read-back matched expected capacity within normal cell tolerance.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging is applied to an uncalibrated cell.

Why the C13 reports wrong battery percentage after a cell swap

The Sugar C13 uses a fuel gauge IC that builds its charge estimate from a stored discharge curve learned on the original cell. When you install a new cell, that stored curve no longer matches the new cell's actual voltage-to-capacity relationship. The IC keeps using the old data, so percentage readouts drift — sometimes reading 100% when the cell is not full, or dropping sharply near 30%. One full discharge-charge cycle with fast charging off forces the IC to relearn the curve against the new cell. After that cycle, percentage accuracy returns to normal.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC has not yet calibrated to the new cell and the phone hits a voltage cliff under screen or modem load. The cell voltage drops below the BMS cutoff threshold — typically around 3.2–3.3V under load — before the displayed percentage reflects the true state of charge. The phone shuts down to protect the cell, even though the percentage shown looks safe. Run one full uninterrupted discharge to below 5% and then charge to 100% without interruption — this resets the coulomb counter baseline and eliminates the premature cutoff.