About this replacement
Xiaomi 12 Pro — 3.87V Li-Polymer Replacement Battery (BP45)
The BP45 is a 3.87V, 4600mAh (17.8Wh) Li-Polymer cell for the Xiaomi 12 Pro smartphone, covering model numbers 2201122C, 2201122G, and 12s Pro. It replaces the original factory cell when capacity has faded or the battery no longer holds a charge. Swapping the BP45 restores full device function across the processor, display, and modem.
- 12 Pro and 12s Pro compatibility: These models share the same battery bay dimensions, connector pinout, and BMS handshake protocol, which is why a single BP45 cell covers the full lineup without modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a 12 Pro unit, confirmed BMS communication was accepted, and verified the charge IC stepped through the correct constant-current and constant-voltage phases without faulting.
- Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve before the coulomb counter locks in reference points that affect percentage accuracy.
Sudden shutdown at 20–30% on the Xiaomi 12 Pro after a cell swap
A new BP45 cell has a discharge curve the fuel gauge IC does not yet know. Under heavy load — 5G modem, high-refresh display, or GPS — the phone draws a current spike the uncalibrated gauge misreads as safe, but the cell voltage drops below the BMS cutoff threshold. The BMS trips and the phone shuts off, even though the percentage read higher. One full discharge-to-charge cycle at standard speed lets the coulomb counter anchor to the real curve and eliminates most false cutoffs.
USB-PD or Xiaomi fast charge not activating on the first cycle after replacement
After a cell swap, the charge IC on the 12 Pro runs a brief handshake with the new BMS before unlocking higher charge rates. On the very first cycle, this handshake can time out and the phone falls back to standard 5W charging. This is normal behaviour — it is not a fault with the charger or cable. Unplug, wait 30 seconds, and reconnect. Fast charging typically activates from the second cycle onward once the BMS has completed its initial negotiation.