Xiaomi Redmi Pro BM4A Compatible Battery 3.85V 4000mAh

Xiaomi Redmi Pro — 3.85V Li-Polymer Replacement Battery (BM4A)

This is a 3.85V, 4000mAh (15.4Wh) Li-Polymer replacement battery for the Xiaomi Redmi Pro smartphone. It fits model numbers 2016020 and 2016021 — the two hardware revisions Xiaomi released under the Redmi Pro line. It replaces the original BM4A cell when capacity has degraded or the battery no longer holds a charge.

• Redmi Pro 2016020 and 2016021 compatibility: Both revisions use the same 3.85V rail, identical connector pinout, and the same BMS handshake protocol. One cell fits both because the fuel gauge IC and charge controller are shared across the two board runs.
• Bench tested on actual hardware: We cycled this cell through the Redmi Pro charge controller and confirmed the BMS accepted the handshake on first connection. The protection circuit tripped correctly at the low-voltage cutoff threshold without false positives at mid-cycle.
• First-cycle fast charge hold-off: On first use after installation, disable fast charging and run one full discharge-charge cycle on standard 5V/1A input. This lets the fuel gauge IC map the new cell's discharge curve before the charge controller pushes higher current into an uncalibrated cell.

Sudden shutdown at 20–30% on the Redmi Pro after a cell swap

This is a voltage cliff issue, not a capacity problem. Under modem activity or screen-on load, the new cell momentarily drops below the shutdown threshold the OS is watching — even though the fuel gauge still shows 20–30%. The fuel gauge IC was calibrated to the old cell's discharge curve and doesn't yet know where the new cell's voltage cliff sits. One full discharge to automatic shutdown, followed by a full charge without interruption, resets the coulomb counter and eliminates most cliff shutdowns.

OS reporting wrong battery percentage after replacement

The Redmi Pro's fuel gauge IC stores a learned discharge curve from the previous cell. When a new cell goes in, the stored curve no longer matches actual cell behaviour, so percentage readings drift — often reading 100% for too long, then dropping fast. This is not a defect in the replacement cell. Force a full discharge to shutdown, then charge uninterrupted to 100% without using the phone. After one complete cycle, the fuel gauge recalibrates against the new cell and percentage accuracy returns to normal.