BP4J Redmi Note 12 Pro+ 5G Replacement Battery 3.87V 4800mAh

Redmi Note 12 Pro+ 5G — 3.87V Li-Polymer Replacement Battery (BP4J)

This 3.87V, 4800mAh (18.58Wh) lithium-polymer cell replaces the OEM BP4J battery in the Redmi Note 12 Pro+ 5G and related Note 12 5G variants. It fits models 22101316UP and 22101316UCP. The dimensions are 85.70 × 65.30 × 5.70mm — same footprint as the factory cell.

• Note 12 5G platform compatibility: The Note 12 Pro+ 5G (22101316UP) and Note 12 5G (22101316UCP) share the same battery bay dimensions, connector pinout, and BMS handshake protocol — one cell covers both models without modification.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on a Note 12 Pro+ 5G unit. The BMS accepted the cell without fault flags, and the charge IC held the CV phase termination at the correct cutoff voltage without truncating early.
• First-cycle fast charge calibration: On first use after installation, disable fast charging for one complete discharge-charge cycle. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current fast charging pushes current into an uncalibrated coulomb counter.

Sudden shutdown at 20–30% on the BP4J replacement cell

The Note 12 Pro+ 5G uses a coulomb counter that was trained on the original cell's internal resistance profile. A new cell has different impedance characteristics, so the fuel gauge IC can misread remaining charge and allow the phone to reach a voltage cliff before the OS sees 0%. Under modem load or display brightness spikes, cell voltage drops below the BMS cutoff threshold while the OS still shows 20–30%. One full slow-charge discharge cycle forces the coulomb counter to recalibrate against the new cell, eliminating the premature cutoff.

USB-PD fast charge not triggering on first cycle after replacement

After a cell swap, the BMS on a freshly installed battery may not complete its handshake with the charge IC on the first plug-in, causing the phone to fall back to standard 5V charging instead of negotiating the higher voltage rail. This is a BMS initialisation state — not a fault with the charger or cable. Fully discharge the phone to auto-shutdown, then charge it uninterrupted to 100% using the original charger. Fast charge negotiation typically restores on the second or third cycle once the BMS has logged a complete charge event.