BM4Q Replacement Battery Xiaomi K30 Pro 3.85V 4400mAh

Xiaomi K30 Pro / K30 Pro 5G — 3.85V Li-Polymer Replacement Battery (BM4Q)

The BM4Q is a 3.85V, 4400mAh Li-Polymer cell that fits the Xiaomi K30 Pro, K30 Pro 5G, and M2004J11G variants. It replaces a degraded or failed original cell and restores the phone to its factory power capacity. Dimensions are 76.40 × 63.20 × 5.20mm — a direct physical match to the battery bay.

• K30 Pro and K30 Pro 5G fit: Both variants share the same battery bay geometry, connector pinout, and BMS handshake protocol. The BM4Q part number covers all three model codes — K30 Pro, K30 Pro 5G, and M2004J11G — without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the K30 Pro platform. The BMS accepted the cell, coulomb counter initialised correctly, and the charge IC held the full 4400mAh capacity without early cutoff.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one full discharge-to-charge cycle at standard current. This lets the fuel gauge IC map the new cell's discharge curve before high-current fast charging pushes load into an uncalibrated counter.

Sudden shutdown at 20–30% on the K30 Pro 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 reads 25% remaining, the actual cell voltage under a modem or display load spike can drop below the hardware cutoff threshold — roughly 3.2V — triggering an abrupt shutdown. This is not a fault in the replacement cell. One full discharge cycle, taken down to automatic shutdown and then charged to 100% without interruption, resets the coulomb counter and closes the gap between reported and actual charge state.

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

On the first charge cycle after a cell swap, the BMS on the new cell may not immediately negotiate the fast charge handshake with the phone's charge IC — the charger falls back to standard 5V input instead. This happens because the BMS starts with conservative current limits until it completes one full cycle and confirms cell health. Charge the battery once at standard speed to 100%, then unplug and reconnect — fast charge should activate on the second cycle once the BMS has cleared its initialisation flag.