Hyundai MB-140 Replacement Battery BL-6900 3.7V 1700mAh

Hyundai MB-140 — 3.7V Li-ion Replacement Battery (BL-6900)

This is a 3.7V, 1700mAh Li-ion battery for the Hyundai MB-140 mobile phone. It replaces OEM part numbers BL-6900 and BP-140. If the original cell no longer holds a charge or the phone shuts down unexpectedly, this cell restores full functionality.

• MB-140 fit confirmation: The MB-140 uses a 3.7V single-cell Li-ion architecture. This cell matches the voltage rail, physical footprint (66.20 × 44.00 × 5.10mm), and connector orientation. The BMS communicates with the phone's charge IC on the same contact layout as the OEM cell.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the MB-140 platform. The BMS accepted the handshake from the phone's charge controller without fault codes, and charge termination triggered correctly at full voltage.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging for the first complete discharge-charge cycle. The phone's fuel gauge IC is calibrated to the old cell's discharge curve. One full cycle at standard current lets it recalibrate against the new cell before high-current charging begins.

Sudden shutdown at 20–30% on the Hyundai MB-140

This is a voltage cliff failure. Under modem transmission or screen load, the cell voltage drops sharply — faster than the fuel gauge IC expects at that state of charge. The phone's protection circuit reads the voltage drop as a low-cell event and cuts power before the percentage reaches zero. It is most common in the first few cycles on a new cell, before the fuel gauge has mapped the actual discharge curve. Running one full discharge-to-shutdown cycle followed by a complete charge resolves it in most cases.

Phone reports wrong battery percentage after cell swap

The MB-140's fuel gauge IC stores a discharge model tied to the previous cell's impedance and capacity curve. Swap the cell and that model no longer matches the new cell's behaviour — so the percentage reading drifts, jumps, or stalls at fixed points. This is not a fault with the replacement cell. Drain the phone fully until it shuts down, then charge uninterrupted to 100% without interruption. After that single cycle, the coulomb counter resets its reference points against the new cell.