About this replacement
Asus Zenfone 2 Deluxe / ZE551ML — 3.85V Li-Polymer Replacement Battery (C11P1424)
This is a 3.85V, 2900mAh (11.17Wh) Li-Polymer battery for the Asus Zenfone 2 Deluxe and related ZE551ML and ZE550ML models. It fits the internal battery slot directly and connects to the same charge management circuit as the original C11P1424 and C11P1423 cells. The fixed internal design means the phone is non-functional once the original cell degrades past usable capacity.
- ZE551ML / ZE550ML platform fit: Both models share the same PCB footprint, connector pinout, and fuel gauge IC handshake. The 77.00 × 53.00 × 4.50mm cell matches the original cavity dimensions and connects to the same coulomb counter without triggering a BMS mismatch error.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on ZE551ML hardware. The BMS accepted charge current without cutoff, and the fuel gauge IC tracked state-of-charge without erratic jumps after the first complete calibration cycle.
- Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle. The fuel gauge IC recalibrates its discharge curve model against the new cell before high-current charging pushes current into an uncalibrated state.
Sudden shutdown at 20–30% on the Zenfone 2 after a cell swap
The ZE551ML's fuel gauge IC retains the discharge curve from the old, degraded cell. When the new cell voltage drops under modem or screen load, the IC misreads the state-of-charge and reports a false percentage until the voltage cliff forces an emergency cutoff. This appears as a sudden shutdown while the percentage still reads 20–30%. One full uninterrupted discharge-to-shutdown followed by a full charge resets the coulomb counter against the new cell's actual curve.
USB charging not starting after the phone sat discharged in storage
If the cell drops below approximately 2.5V during storage, the BMS enters lockout mode and the phone will not respond to a standard USB connection. The charge IC requires a trickle pre-charge current to bring the cell above the lockout threshold before normal charging resumes. Connect the phone to a wall adapter — not a PC USB port — and leave it undisturbed for 20–30 minutes without expecting any screen response. Once the cell clears roughly 3.0V, the BMS releases the lockout and charging proceeds normally.