Asus ZenFone 3 5.2 C11P1601 Replacement Battery 3.85V 2500mAh

Asus ZenFone 3 5.2 / ZE520KL — 3.85V Li-Polymer Replacement Battery (C11P1601)

This is a 3.85V, 2500mAh Li-Polymer cell that replaces the original C11P1601 battery in the Asus ZenFone 3 5.2 and ZE520KL. It fits ZE520KL variants including ZenFone 3 Dual SIM Global LTE. Capacity matches the factory spec at 9.63Wh.

• ZE520KL and Dual SIM Global LTE fitment: Both variants share the same battery bay dimensions, connector pinout, and BMS communication protocol — one cell fits all listed models without modification.
• Bench tested on actual hardware: We cycled this cell through a full charge and load discharge on ZE520KL hardware. The BMS handshake completed correctly, charge current stepped down at 4.35V as expected, and the protection circuit tripped cleanly at the low-voltage cutoff.
• First-cycle fuel gauge reset on the ZE520KL: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard current. This lets the fuel gauge IC map the new cell's discharge curve before the charge IC begins pushing higher current into an uncalibrated cell.

Sudden shutdown at 20–30% on the ZE520KL after a cell swap

This happens because the ZenFone 3's fuel gauge IC still holds the discharge curve of the old, degraded cell. The new cell hits a voltage cliff under modem or display load at a state-of-charge the IC has not yet mapped correctly. The phone reads 25% but the actual cell voltage has already dropped below the shutdown threshold. One full discharge-charge cycle at standard current rewrites the coulomb counter baseline and clears this behaviour.

USB fast charge not activating on the first cycle after replacement

After fitting a new cell, the charge IC on the ZE520KL may default to standard 5V/1A input until it confirms the BMS is responding within expected parameters. On a fresh cell with no charge history, the proprietary fast-charge handshake can be skipped on the first cycle. Complete one full standard charge first — the IC logs the cell's internal resistance and re-enables the fast-charge protocol from the second cycle onward. Confirm fast charge is active by checking the notification shade for the fast-charging indicator at 5V/2A or above.