BLU Dash Jr 4.0 K Replacement Battery 3.7V 1500mAh C785039150J

BLU Dash Jr 4.0 K / D143K — 3.7V Li-ion Replacement Battery (C785039150J)

This is a 3.7V, 1500mAh Li-ion replacement battery for the BLU Dash Jr 4.0 K (D143K) smartphone. It slots into the original battery bay and restores power to calls, messaging, and apps. Capacity is 1500mAh (5.55Wh), matching the OEM cell specification.

• Dash Jr 4.0 K / D143K fit: Both model numbers reference the same hardware platform — same battery bay dimensions (77.95 × 49.88 × 4.00mm), same 3.7V voltage rail, and the same connector pinout. One cell covers both designations.
• Bench tested on actual hardware: We ran charge and discharge cycles through a full charge sequence and confirmed the BMS accepted charge current without tripping overcurrent protection. Charge termination voltage held at the correct 4.2V cutoff.
• Fuel gauge recalibration after swap: On first use after installing this cell, run one complete discharge down to auto-shutdown, then charge uninterrupted to 100%. This gives the phone's fuel gauge IC a full reference curve on the new cell before normal use begins. Skip this step and the percentage readout may drift by 10–15%.

Why the Dash Jr 4.0 K reports wrong battery percentage after a cell swap

The D143K uses a coulomb-counter-based fuel gauge IC that builds its discharge model against the cell it last fully cycled. When you install a new cell, the IC still references the old degraded cell's curve — so the percentage it shows can be off by 10–20% in either direction. The fix is one full uninterrupted discharge-to-shutdown followed by a full charge. After that single reference cycle, the IC locks onto the new cell's actual capacity and percentage accuracy returns to normal.

Sudden shutdown at 20–30% remaining on the replacement cell

This happens when the fuel gauge IC hasn't recalibrated and the phone's displayed percentage no longer matches the cell's real state of charge. Under modem or screen load, voltage drops sharply below the 3.4V protection threshold — triggering an emergency shutdown even though the display still showed charge remaining. It's not a faulty cell; it's a calibration mismatch. Run one full discharge-charge cycle and the shutdown point will align with the true low-voltage cutoff near 3.2–3.4V.