About this replacement
Asus ZenFone 3 Deluxe 5.5 / ZS550KL — 3.85V Li-Polymer Replacement Battery (C11P1603)
This is a 3.85V, 3300mAh lithium-polymer cell for the Asus ZenFone 3 Deluxe 5.5, ZenFone 3 Deluxe 5.5 Dual SIM, and ZS550KL. It replaces the original C11P1603 pack when the existing cell no longer holds a charge through normal daily use. Rated at 12.71Wh, it matches the voltage and form factor the phone's charge IC expects.
- ZS550KL and Dual SIM compatibility: Both variants share the same battery bay dimensions, connector pinout, and BMS handshake. The ZS550KL designation covers both single and Dual SIM models — the charge controller does not differentiate between them.
- Bench tested on actual hardware: We ran this cell on a ZS550KL unit and confirmed the BMS accepted the pack without a fault flag. The charge IC entered CC/CV charging normally, and the fuel gauge IC began tracking state-of-charge from the first cycle.
- First-cycle fast charge protocol: On first use after installation, disable fast charging for one full discharge-charge cycle. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current charging pushes current into an uncalibrated state.
Why the ZenFone 3 Deluxe reports wrong battery percentage after a cell swap
The ZS550KL uses a coulomb-counter-based fuel gauge IC that builds its state-of-charge model against the original cell's discharge curve. When a new cell goes in, the IC is still reading against the old curve — so the percentage shown can be off by 10–20%. The fix is one complete discharge down to automatic shutdown, followed by a full charge without interruption. After that cycle, the fuel gauge recalibrates and the percentage readout stabilises.
Sudden shutdown at 20–30% remaining on the ZS550KL
This happens when the cell voltage drops below what the modem or display backlight needs under peak load, even though the fuel gauge still shows capacity remaining. It is a voltage-cliff issue — the cell cannot sustain the voltage rail under high-draw moments like LTE reconnection or screen-on bursts. The fuel gauge IC has not yet mapped the new cell's internal resistance, so it misjudges remaining capacity. Run one full discharge-charge cycle and the cutoff threshold will align more accurately with actual cell voltage.