Asus ZenFone Max M2 Replacement Battery C11P1805 3.85V 3900mAh

Asus ZenFone Max M2 — 3.85V Li-Polymer Replacement Battery (C11P1805)

This 3.85V, 3900mAh (15.02Wh) Li-Polymer battery replaces the original C11P1805 cell in the Asus ZenFone Max M2, ZenFone Max M2 Dual SIM, and ZB633KL. It fits the slot directly and connects to the same charge IC and fuel gauge circuitry as the factory cell. Use it to recover a phone that no longer holds a charge or has a swollen, damaged battery.

• ZB633KL and Dual SIM compatibility: Both variants run the same 3.85V power rail, use the same flex connector pinout, and handshake with the same BMS logic — one cell covers all three listed models without any wiring or firmware difference.
• Bench tested on actual hardware: We cycled this cell through charge, load, and cutoff sequences on a ZB633KL unit. The BMS accepted the cell on the first cycle, charge current tapered correctly at full capacity, and the low-voltage cutoff triggered at the expected threshold with no false trips.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging and run one full discharge-to-charge cycle at standard current. The ZenFone Max M2's fuel gauge IC is calibrated to the old cell's discharge curve — one slow cycle lets it map the new cell before high-current charging starts.

Sudden shutdown at 20–30% on the ZenFone Max M2

This is a voltage cliff symptom, not a capacity problem. When the modem fires a high-data burst or the screen hits peak brightness, current draw spikes sharply. A degraded or freshly swapped cell that hasn't been calibrated can't sustain the voltage under that load, so the phone shuts off even though the gauge still shows charge remaining. The fix is one full discharge-charge cycle at standard current to let the fuel gauge IC remap the new cell's actual voltage curve. After that cycle, the OS reads the remaining charge accurately and shuts down at the correct threshold near 3.0V per cell.

Phone won't power on after sitting in storage with a flat battery

If the ZenFone Max M2 has been stored for weeks or months with a depleted cell, the BMS may have locked out below 2.5V to prevent damage — the phone won't respond to the power button or show a charging indicator. Plug in a charger and leave it connected for 15–20 minutes without pressing anything; the charge IC trickle-charges the cell back above the BMS unlock threshold. Once the cell reaches approximately 2.8–3.0V, the BMS re-initialises and the phone boots or shows the charging screen normally.