T-Mobile MF64 Replacement Battery 3.8V 2300mAh Li3823T43P3h735350

T-Mobile MF64 / Z64 4G HotSpot — 3.8V Li-ion Replacement Battery (Li3823T43P3h735350)

This is a 3.8V, 2300mAh (8.74Wh) Li-ion replacement battery for the T-Mobile MF64, Z64, and Z64 4G HotSpot. It slots directly into these ZTE-based devices where the original cell has aged past usable capacity. The OEM part number Li3823T43P3h735350 confirms fitment across all three listed models.

• MF64, Z64, and Z64 4G HotSpot compatibility: All three models run the same 3.8V cell platform with an identical connector and BMS handshake. Swapping between models on this battery is straightforward — same footprint at 72.90 × 53.60 × 4.70mm, same charging profile.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the MF64 platform. The BMS accepted the charge IC handshake without prompting a fault flag, and voltage held stable under concurrent Wi-Fi and modem load without triggering cutoff.
• Fuel gauge recalibration on first use: After installation, disable fast charging and run one full discharge-charge cycle before resuming normal use. The fuel gauge IC on this platform calibrates its coulomb counter against the cell's discharge curve on first cycle — skipping this step causes the OS to report inaccurate percentages until recalibration completes.

Sudden shutdown at 20–30% on the Z64 after a cell swap

This happens because the fuel gauge IC is still referencing the discharge curve of the original aged cell, not the new one. When the device hits a voltage point that mapped to ~20–30% on the old cell, it signals shutdown — even though the new cell has capacity left. The fix is one complete discharge down to automatic power-off, followed by a full uninterrupted charge to 100%. After that cycle, the coulomb counter resets its reference curve to the replacement cell and the shutdowns stop.

Device not powering on after the replacement battery sat in storage

Li-ion cells shipped or stored for extended periods can fall below 2.5V per cell, triggering BMS lockout as a protection against over-discharge damage. The MF64 and Z64 will show no response — no boot, no charge indicator — when the BMS is in lockout state. Connect to a wall charger (not a USB port) and leave it for 20–30 minutes without pressing the power button. The charge IC will trickle current into the cell until voltage clears the 2.5V threshold, at which point the BMS re-initialises and the device boots normally.