Meizu BT51 MX5 Replacement Battery 3.8V 3050mAh

MeiZu MX5 / M575 Series — 3.8V Li-Polymer Replacement Battery (BT51)

The BT51 is a 3.8V, 3050mAh (11.59Wh) Li-Polymer cell for the MeiZu MX5, MX5 Dual SIM, M575 Dual SIM, and M575M. It replaces the original battery when the device shuts down early, charges slowly, or no longer holds a usable charge. Capacity figure is taken from the product data — not inflated.

• MX5 and M575 platform fit: The MX5 and M575 variants share the same battery bay dimensions, connector pinout, and BMS handshake protocol. One BT51 cell covers the full range — 68.00 × 62.46 × 4.93 mm, flat-pack Li-Polymer format with the same three-pin flex connector used across both models.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on an MX5 unit. The BMS accepted the cell without error flags, protection circuits tripped correctly at low-voltage threshold, and the charge IC handed off to trickle at the expected voltage ceiling.
• Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging for one complete discharge-charge cycle. The fuel gauge IC is still calibrated to the old cell's discharge curve. Running one slow cycle lets it remap against the new cell before high-current charging pushes into an uncalibrated state.

Sudden shutdown at 20–30% on the MX5 after a cell swap

This happens because the fuel gauge IC still holds the old cell's voltage-to-capacity curve in memory. When screen brightness and the modem pull current simultaneously, the new cell's actual terminal voltage drops below the shutdown threshold before the gauge registers low battery. The phone cuts out while the percentage display still reads 20% or higher. One full slow discharge-charge cycle — no fast charge — forces the coulomb counter to re-anchor against the new cell's actual curve, and the early shutdowns stop.

MeiZu MX5 not powering on after storage with a new BT51 installed

If the replacement cell was stored in a discharged state before shipping, its resting voltage may have dropped below 2.5V per cell — the BMS hard lockout threshold. At that point the phone shows nothing when connected to a charger. Connect to a wall adapter at 5V and leave it for 15–20 minutes without pressing the power button. The charge IC trickle-feeds current until the cell climbs above the BMS re-enable threshold, typically around 2.9V, at which point normal charging resumes and the device will power on.