About this replacement
Asus ZenFone 8 ZS590KS — 3.87V Li-Polymer Replacement Battery (C11P2003)
This is a 3.87V, 3900mAh (15.09Wh) Li-Polymer cell for the Asus ZenFone 8 (ZS590KS). It replaces OEM part numbers C11P2003 and 0B200-03950000. Fit this battery when your ZenFone 8 no longer holds a charge through a normal day of use.
- ZenFone 8 / ZS590KS fitment: Both model references — ZenFone 8 and ZS590KS — share the same physical cell format, connector pinout, and BMS handshake. One replacement covers both designations.
- Bench tested on actual hardware: We ran this cell through charge and discharge on ZS590KS hardware. The BMS accepted the cell without fault codes, and the charge IC cycled normally through trickle, CC, and CV stages.
- First-cycle fast charge protocol: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate its coulomb counter against the new cell's actual discharge curve before high-current charging pushes into an uncalibrated register.
Sudden shutdown at 20–30% on the ZenFone 8 after a cell swap
A new cell has a discharge curve the fuel gauge IC has never seen before. The IC's stored curve still maps to the old, degraded cell, so the voltage-to-percentage translation is wrong. Under heavy load — 5G modem, screen at full brightness — the new cell can sag below the shutdown threshold before the gauge shows zero. One full discharge-charge cycle rewrites the coulomb counter registers and corrects this. After calibration, shutdowns below 20% stop.
USB-PD fast charge not triggering on the first cycle after replacement
After fitting a new cell, the charge IC sometimes defaults to standard 5V/1A input and won't negotiate USB-PD or HyperCharge rates. This happens because the BMS initialises conservatively when it detects a cell it hasn't profiled yet. Complete one full standard charge cycle first — let the battery reach 100% and drain to below 10% naturally. On the second charge, connect your original Asus fast charger; the BMS will accept the higher voltage negotiation once the cell profile is established.