Xiaomi BM5S K60 Ultra Replacement Battery 3.88V 4850mAh

Xiaomi K60 Ultra / K60 / 13T Pro — 3.88V Li-Polymer Replacement Battery (BM5S)

The BM5S is a 3.88V, 4850mAh (18.82Wh) Li-Polymer cell that fits the Xiaomi K60 Ultra, K60, and 13T Pro. It replaces a degraded original battery that can no longer hold a stable voltage under display, modem, or processor load. Physical dimensions are 85.40 × 64.60 × 6.00mm — confirm fitment before installation.

• K60 Ultra, K60, and 13T Pro fitment: These three models share the same battery bay geometry, connector pinout, and BMS handshake protocol — all three accept the BM5S cell without modification to the flex cable or connector orientation.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the K60 platform and confirmed the BMS accepted the handshake, the fuel gauge IC began tracking capacity, and charge current ramped correctly through each charging stage.
• First-cycle fast charge behaviour: On first use after installation, disable Xiaomi's HyperCharge for one full discharge-charge cycle. This lets the fuel gauge IC recalibrate its coulomb counter against the new cell's discharge curve before high-current fast charging pushes elevated current into an uncalibrated cell.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff, not a capacity fault. The fuel gauge IC carries over calibration data from the old degraded cell and misjudges when the new cell's voltage will drop below the processor's minimum rail. Under peak modem or screen load, the phone pulls enough current to collapse voltage faster than the gauge predicts. Run one complete discharge to automatic shutdown, then charge uninterrupted to 100% — this resets the coulomb counter to the new cell's actual discharge curve. After that cycle, the gauge tracks correctly and shutdowns at low percentage stop.

HyperCharge not activating after battery replacement

Xiaomi's proprietary fast charge protocol negotiates with the battery BMS before the charge IC ramps current above standard 5V input. On the first cycle with a new cell, the BMS may not complete that negotiation and the phone defaults to standard charge rates instead. This is not a fault — it clears after the fuel gauge completes its first full calibration cycle. Charge once to 100% on standard charging, then reconnect the HyperCharge adapter and the protocol handshake will complete normally at approximately 4.35V cell voltage.