About this replacement
Asus ZenFone 5 A500 / A501 — 3.8V Li-Polymer Replacement Battery (C11P1324)
This is a 3.8V, 2100mAh Li-Polymer cell replacing OEM part C11P1324 in the Asus ZenFone 5 lineup. It fits the ZenFone 5, ZenFone 5 A500, ZenFone 5 A501, ZenFone 5 LTE, and related variants. Dimensions are 63.48 × 53.32 × 4.29mm — match these against your original cell before installation.
- ZenFone 5 series fitment: The A500, A501, and LTE variants share the same battery bay dimensions and connector pinout. All run the same 3.8V nominal rail, so one cell covers the full range without BMS handshake conflicts.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on ZenFone 5 hardware. The BMS accepted charge from the device's charge IC without flagging errors, and cell voltage held stable across screen-on and modem-active load states.
- Fuel gauge recalibration on first use: After fitting this cell, disable fast charging and run one full discharge-to-charge cycle before normal use. This lets the ZenFone 5's fuel gauge IC map the new cell's discharge curve accurately — skipping this step causes erratic percentage readings for the first several cycles.
Why the ZenFone 5 reports wrong battery percentage after a cell swap
The ZenFone 5 uses a coulomb counter that stores learned charge data from the original cell. When you swap in a new cell, that stored curve no longer matches the new cell's chemistry profile. The OS reads a percentage based on stale data, so it may show 80% and drop to 20% minutes later. One full discharge from 100% to shutdown, followed by a complete uninterrupted charge, forces the fuel gauge IC to re-anchor its endpoints to the new cell.
Sudden shutdown at 20–30% on the replacement cell
This happens when the cell voltage drops below the modem's sustained-load threshold before the OS gauge reaches 0%. Under LTE or Wi-Fi transmit bursts, current draw spikes and the cell — still mid-calibration — cannot hold voltage above the BMS cutoff floor. The phone cuts out even though the gauge shows charge remaining. Run the recalibration cycle first, then check that shutdown moves toward the 5–10% range. If it persists below 15%, measure resting cell voltage at reported 30%: it should read above 3.6V.