Consumer Cellular Envoy U3900 Compatible Battery 3.7V 700mAh

Consumer Cellular Envoy U3900 — 3.7V Li-ion Replacement Battery

This 3.7V, 700mAh lithium-ion battery replaces the original cell in the Consumer Cellular Envoy U3900 smartphone. It fits the standard battery bay and matches the original connector and form factor at 53.78 × 34.05 × 4.80mm. Use this when the existing cell no longer holds a usable charge or has swollen and needs to come out.

• Envoy U3900 fitment: The U3900 uses a removable, single-cell 3.7V Li-ion pack in a compact chassis built around basic voice and messaging loads. This replacement matches that voltage rail and physical slot — no modification needed.
• Bench tested on actual hardware: We cycled this cell through charge and discharge under a controlled load. The BMS held cutoff at the expected low-voltage threshold and the charge IC accepted the cell without fault flags on the first cycle.
• Fuel gauge recalibration after swap: On first use after installing this cell, run one complete discharge down to auto-shutoff, then charge to 100% uninterrupted. This gives the fuel gauge IC a full reference curve against the new cell before normal use resumes.

Why the U3900 reports wrong battery percentage after a cell swap

The U3900 tracks charge state through a fuel gauge IC that builds its model from previous discharge cycles. When a new cell goes in, the IC still references the old cell's curve. The percentage readout drifts — often showing more charge than is actually present. One full discharge-to-shutoff followed by a complete charge resets the coulomb counter and brings the reported percentage back in line with real capacity.

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

This happens when the cell voltage drops below the modem's minimum operating threshold under transmit load, even though the fuel gauge still reads significant charge. A 700mAh cell at this size has a steeper voltage-versus-capacity curve in the lower third. The phone's power manager trips before the gauge catches up. If this persists after one full calibration cycle, check that the cell seated fully and the contact pins are clean — poor contact raises internal resistance and accelerates that voltage sag. Target a resting open-circuit voltage of 3.7V after a full charge to confirm the cell is healthy.