About this replacement
Xiaomi Mi 6X / Mi A2 — 3.85V Li-Polymer Replacement Battery (BN36)
This is a 3000mAh, 3.85V Li-Polymer replacement battery for the Xiaomi Mi 6X and Mi A2 smartphones. It uses OEM part number BN36 and fits the standard Mi 6X body cavity at 85.08 x 64.50 x 3.45mm. It restores capacity to devices that have degraded through charge cycles or age.
- Mi 6X and Mi A2 compatibility: Both devices share the same PCB layout, battery connector pinout, and BMS handshake protocol. The Mi A2 is the global variant of the Mi 6X — same chassis, same battery slot, same BN36 spec.
- Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on Mi 6X units. The BMS accepted the cell without error flags, and the fuel gauge IC tracked state-of-charge without interruption across the test cycles.
- First-cycle fast charge protocol: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current charging pushes into an uncalibrated state.
Why the Mi 6X reports wrong battery percentage after a cell swap
The Mi 6X uses a coulomb counter in the fuel gauge IC that tracks charge based on the previous cell's discharge curve. When a new cell goes in, that stored curve no longer matches the actual cell chemistry. The IC keeps using the old reference, which causes the displayed percentage to lag or jump. One full discharge-to-shutdown followed by a complete charge to 100% forces the IC to rewrite its calibration against the new cell.
Sudden shutdown at 20–30% on the replacement cell
This happens when the cell voltage drops below the BMS cutoff threshold under load — typically during modem activity, screen-on bursts, or app wake cycles. The fuel gauge still reads 25%, but the cell cannot sustain the voltage rail under that current draw. The BMS trips as a protection event, not a capacity failure. Charge the phone fully, then run one complete cycle without fast charging — if shutdowns stop, the fuel gauge has recalibrated. If they continue, check that the cell connector is fully seated and making clean contact.