Hyundai MBD125 Compatible Battery 3.7V 750mAh Li-ion

Hyundai MBD125 / MBD125 Dual Sim — 3.7V Li-ion Replacement Battery

This 3.7V 750mAh (2.78Wh) lithium-ion cell is a direct swap for the battery in the Hyundai MBD125 and MBD125 Dual Sim smartphones. It matches the original cell's footprint at 53.00 × 33.90 × 5.70mm, so it seats correctly in the battery bay without modification. Voltage and capacity match OEM spec — the fuel gauge IC reads it without recalibration errors on first boot.

• MBD125 and MBD125 Dual Sim fitment: Both variants use the same battery bay dimensions and 3.7V single-cell architecture. The connector pinout and BMS handshake are identical across both models, so one cell covers either configuration without adapter or modification.
• Bench tested on actual hardware: We cycled this cell through full discharge and charge on the MBD125 platform. The BMS accepted the cell on first insertion, charge termination triggered at the correct cutoff voltage, and the fuel gauge IC tracked state of charge without jumping erratically through the first cycle.
• First-cycle fast charge tip: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate its coulomb counter against the new cell's discharge curve before high-current charging pushes into an uncalibrated state.

Sudden shutdown at 20–30% on the MBD125 after a cell swap

The MBD125 fuel gauge IC stores a discharge curve calibrated to the old cell. A new cell with a slightly different internal resistance profile causes the IC to misread remaining capacity. Under load spikes from the modem or display, the actual cell voltage drops below the shutdown threshold even though the gauge still reads 20–30%. One full discharge-to-cutoff cycle followed by an uninterrupted charge to 100% allows the coulomb counter to rebuild its curve against the new cell. After that cycle, the reported percentage aligns with actual voltage and load-induced shutdowns stop.

MBD125 not powering on after the replacement battery sat in storage

Lithium-ion cells self-discharge during storage. If the cell voltage drops below approximately 2.5V, the BMS enters lockout mode and blocks current flow to protect the cell from damage. The phone shows no response — no boot screen, no charge indicator — because the BMS will not pass voltage to the board. Connect to a charger and leave it for 15–20 minutes without pressing the power button. The charge IC will trickle current into the cell until voltage climbs above the BMS re-enable threshold, at which point the charge indicator should appear and normal charging resumes.