About this replacement
Asus ZenFone 3s Max — 3.85V Li-Polymer Replacement Battery (C11P1614)
This 3.85V, 5000mAh Li-Polymer cell replaces the original C11P1614 battery in the Asus ZenFone 3s Max. It fits the ZC521TL, ZenFone 3s Max Dual SIM TD-LTE IN, and ZenFone Pegasus 3S variants. Rated at 19.25Wh, it matches the factory spec so the phone's charge IC operates within its intended parameters.
- ZC521TL and Pegasus 3S fitment: These variants share the same 3.85V power rail, connector pinout, and BMS handshake as the standard ZenFone 3s Max, so one cell covers all listed models without adapter or modification.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on a ZC521TL unit. The BMS accepted the charge IC handshake on the first cycle, held voltage through heavy screen-on load, and tripped no protection cutoffs.
- Fuel gauge recalibration on first use: Disable fast charging for the first complete discharge-charge cycle after installation. The ZenFone 3s Max uses a coulomb counter that calibrated its curve against the old cell — running one slow cycle gives the fuel gauge IC accurate endpoints before fast charge current is applied.
Why the ZenFone 3s Max reports wrong battery percentage after a cell swap
The ZenFone 3s Max uses a coulomb counter that tracks charge flow relative to a stored discharge curve from the original cell. When a new cell goes in, the counter still references that old curve, so percentages drift from the actual state of charge. The gauge does not auto-reset — it needs at least one full cycle from 100% charge down to automatic shutdown and back to full. After that single cycle, the reported percentage aligns closely with real cell voltage across the 3.85V nominal range.
Sudden shutdown at 20–30% on the replacement cell
This happens when the fuel gauge IC has not yet mapped the new cell's voltage cliff. Li-Polymer cells drop voltage steeply below roughly 3.5V per cell, and the modem or display load can pull the cell below that threshold faster than the uncalibrated counter expects. The phone interprets this as a hard undervoltage event and cuts power before the reported percentage reaches zero. Run one full discharge cycle to let the gauge learn the new cliff point — after calibration, shutdowns below 15% stop occurring.