USCellular SCH-R390 Replacement Battery 3.7V 900mAh Li-ion

USCellular SCH-R390 / Freeform 4 — 3.7V Li-ion Replacement Battery

This 3.7V, 900mAh Li-ion battery fits the USCellular SCH-R390, Freeform 4, SCH-R640, and Character handsets. It replaces the original cell when the phone no longer holds a charge through a normal day of calls and messaging. Dimensions are 54.72 x 41.80 x 4.50mm — confirm these against your existing battery before installing.

• SCH-R390 / Freeform 4 / SCH-R640 / Character platform fit: These four models share the same battery bay dimensions, contact pitch, and connector orientation. One cell covers all four without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS held voltage within the expected 3.7V nominal range and cut off cleanly at low-voltage threshold without tripping a lockout condition.
• Fuel gauge recalibration on first use: After installing this cell, run one complete discharge-charge cycle with fast charging disabled. The phone's fuel gauge IC calibrated to the old cell's discharge curve — it needs one full cycle against the new cell before percentage readings stabilise.

Sudden shutdown at 20–30% on the SCH-R390 after a cell swap

The SCH-R390's fuel gauge IC stores a learned discharge curve from the previous cell. When you install a new cell, the IC still references that old curve and miscalculates the voltage cliff. Under modem load — an active call or data burst — the cell voltage drops faster than the IC predicts, and the phone shuts off before the reported percentage reaches zero. Running one full discharge cycle down to automatic shutdown, then charging to 100% uninterrupted, forces the coulomb counter to remap against the new cell's actual capacity. After that cycle, the reported percentage aligns with real remaining charge.

Phone feels warm near the battery on the first charge after replacement

A new cell starts with higher internal impedance than a broken-in cell. The charge IC pushes current into that higher-impedance cell, and the resistance converts more energy to heat than it would on a cycled battery. This is normal and typically resolves within two to three charge cycles as the cell's impedance settles. If the phone stays warm after three full cycles, check that the battery contacts are seated flush and that no debris is raising contact resistance — measure voltage at the contacts and expect 3.7V nominal at 50% state of charge.