About this replacement
Xiaomi Redmi 10X — 3.85V Li-Polymer Replacement Battery (BM4S)
The BM4S is a 4500mAh, 3.85V lithium-polymer cell built to replace the factory battery in the Xiaomi Redmi 10X (M2004J7AC). It matches the OEM footprint at 72.60 × 64.10 × 5.20mm, so it sits flush in the chassis without modification. Capacity is rated at 17.33Wh — identical to the original specification.
- Redmi 10X / M2004J7AC fit: Both model references use the same battery bay geometry, connector pinout, and BMS handshake protocol. One cell covers both variants without adapter or modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the Redmi 10X platform. The BMS accepted the full 4500mAh charge curve without tripping an overvoltage cutoff, and the fuel gauge IC tracked state-of-charge correctly after a complete calibration cycle.
- First-cycle fuel gauge calibration: On first use after installation, disable fast charging and run one full discharge-to-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve before the charge IC starts pushing high-current fast-charge loads into an uncalibrated cell.
Sudden shutdown at 20–30% on the Redmi 10X after a cell swap
This happens because the fuel gauge IC is still using the discharge curve it learned from the old, degraded cell. A fresh 4500mAh cell holds a steeper voltage slope in the 20–30% range than a worn cell does. The phone's charge controller reads that voltage drop as empty and triggers a protection shutdown before the cell is actually depleted. One full discharge cycle — draining to automatic power-off, then charging uninterrupted to 100% — recalibrates the coulomb counter against the new cell's actual curve and stops the premature cutoff.
USB-PD fast charge not activating on the first cycle after replacement
Xiaomi's fast-charge handshake runs a brief BMS negotiation check before the charge IC ramps current. On a brand-new cell, the BMS may return a conservative impedance reading that causes the charge IC to fall back to standard 5V charging for the first session. This is not a fault — it self-resolves after one standard charge completes and the BMS has a baseline impedance reference. If fast charge still does not activate after two full cycles, check the charging cable and adapter for USB-PD compliance, as the BM4S BMS on this platform requires a certified 18W or higher adapter to trigger the protocol.