Xiaomi Mi Mix 3 BM3K Replacement Battery 3.85V 2650mAh

Xiaomi Mi Mix 3 — 3.85V Li-Polymer Replacement Battery (BM3K)

This is a 3.85V, 2650mAh Li-Polymer replacement battery for the Xiaomi Mi Mix 3 smartphone. It fits models M1810E5E, M1810E5C, and the broader Mix 3 series that share the BM3K form factor and connector pinout. Install it when the original cell no longer holds a usable charge or the phone shuts down unexpectedly under load.

• Mix 3 series compatibility: The M1810E5E and M1810E5C variants share an identical battery bay, connector, and BMS handshake. The same BM3K cell fits all of them — no adapter or pin modification needed.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the Mix 3 platform. The BMS accepted the cell without fault flags, and the charge IC stepped through CC/CV phases correctly.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one full discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell.

Sudden shutdown at 20–30% on the Mix 3 after a cell swap

A new Li-Polymer cell has a slightly different voltage-to-capacity curve than the aged cell the fuel gauge IC was trained on. When the phone draws a surge current — modem transmit, screen brightness spike — the new cell's terminal voltage drops sharply under load. The system reads that drop as a hard low-battery cutoff and shuts down, even though the coulomb counter still shows 20–30% remaining. One full discharge-to-shutdown and uninterrupted charge cycle retrains the IC. After that cycle, the reported percentage tracks actual cell voltage accurately.

USB-PD or fast charge not activating on the first cycle after replacement

Xiaomi's charge protocol negotiation runs between the charger, the charge IC, and the BMS. On the very first charge after a cell swap, the BMS may report an unverified cell state, causing the charge IC to fall back to standard 5V/1A input as a precaution. This is not a fault with the battery or the charger. Complete one full slow charge to 100% and allow the phone to read the cell at rest. Fast charging resumes normally from the second cycle onward once the BMS clears the unverified-cell flag.