Asus ZenFone 4 C11P1618 Replacement Battery 3.85V 3200mAh

Asus ZenFone 4 ZE554KL — 3.85V Li-Polymer Replacement Battery (C11P1618)

This is a 3.85V, 3200mAh Li-Polymer cell (12.32Wh) replacing the original C11P1618 battery in the Asus ZenFone 4. It fits the ZE554KL variant specifically — not other ZenFone 4 variants with different form factors. Install it when the original cell no longer holds a charge or causes unexpected shutdowns.

• ZE554KL fitment: The ZenFone 4 ZE554KL uses a specific 81.65 × 65.40 × 3.15mm cell footprint with a matching connector pinout tied to the phone's fuel gauge IC. This cell matches those dimensions and the OEM part number C11P1618 exactly — no physical modification needed to seat it.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the ZE554KL board. The BMS accepted the cell without flagging an error, and the charge IC ramped current normally from trickle to full CC/CV profile.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging for the first complete discharge-charge cycle. The ZenFone 4's fuel gauge IC was calibrated to the old cell's discharge curve — running one slow cycle first lets it map the new cell before high-current charging is applied.

Why the ZenFone 4 shuts down suddenly at 20–30% after a cell swap

A new cell has a slightly different voltage-discharge curve than the worn cell the fuel gauge IC was trained on. At 20–30% reported charge, the IC may read a voltage that triggers the low-battery cutoff — even though the new cell still has capacity available. The phone interprets the voltage drop under load (modem transmit or screen-on peaks) as a near-empty state and cuts power. One full slow discharge-charge cycle forces the coulomb counter to relearn the new cell's curve and eliminates the false cutoff threshold.

USB-PD fast charge not activating on the first cycle after replacement

After fitting a new cell, the ZenFone 4's charge controller sometimes defaults to standard 5V charging rather than negotiating the higher voltage rail. This happens because the BMS treats an uncalibrated cell as an unknown state and withholds fast-charge handshake approval as a protection measure. Let the phone complete one full charge to 100% on a standard charger first. On the second charge cycle, fast charging typically resumes as the BMS confirms cell impedance is within the expected range.