Xiaomi Mi CC9e BM4F Replacement Battery 3.85V 3950mAh

Xiaomi Mi CC9e — 3.85V Li-Polymer Replacement Battery (BM4F)

This is a 3950mAh Li-Polymer cell built to the BM4F specification for the Xiaomi Mi CC9e and its regional variants. It fits the Mi CC9e Standard Edition, the Dual SIM variant, and the M1906F9SC — all of which share the same battery bay and connector pinout. Voltage is 3.85V nominal; full pack energy is 15.21Wh.

• Mi CC9e variant coverage: The Standard Edition, Standard Edition Dual SIM, and M1906F9SC all use the same BM4F footprint — same connector, same BMS handshake, same charge IC protocol. One cell covers the full regional lineup.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a CC9e unit. The BMS accepted the charge IC handshake cleanly, protection circuits tripped correctly at low-voltage cutoff, and the fuel gauge IC tracked state-of-charge without error flags after the first full cycle.
• First-cycle fuel gauge reset: After installation, disable fast charging and run one complete discharge down to auto-shutdown, then charge to 100% on standard 5V. This lets the coulomb counter recalibrate its discharge curve against the new cell before high-current fast charging begins pushing variable current into an uncalibrated gauge.

Why the CC9e reports wrong battery percentage after a cell swap

The CC9e uses a fuel gauge IC that builds its state-of-charge model against the discharge curve of the original cell. When a new cell goes in, that stored curve no longer matches actual cell chemistry, so the reported percentage drifts — often reading 30% when the phone is close to shutdown. The gauge needs a full reference cycle to relearn the new cell's voltage-to-capacity relationship. One slow discharge to cutoff followed by a full charge resolves it. After that cycle, percentage reporting stabilises.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops below the modem or display load threshold before the fuel gauge has recalibrated. The phone sees 25% on the gauge but the actual cell voltage collapses under peak draw — the BMS trips protection and the phone cuts off. It is not a faulty cell; it is an uncalibrated coulomb counter. Run the first-cycle reset: discharge fully to auto-shutdown, then charge uninterrupted to 100% at standard 5V. After one complete reference cycle, the gauge tracks actual cell voltage and shutdowns at low percentage stop.