AT&T RADIANT Core Replacement Battery LT25H426271W 3.85V

AT&T RADIANT Core / Calypso — 3.85V Li-Polymer Replacement Battery (LT25H426271W)

This is a 3.85V, 2700mAh lithium-polymer cell built to replace the original LT25H426271W battery in the AT&T RADIANT Core and Calypso smartphones. It fits the U304AA and U319AA model numbers directly. Capacity figure is taken from product specifications — 10.4Wh total energy.

• RADIANT Core and Calypso shared battery platform: The U304AA (RADIANT Core) and U319AA (Calypso) run the same 3.85V battery rail, use the same connector footprint, and share the LT25H426271W part number — one cell fits both without any modification.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge passes on the RADIANT Core platform. The BMS accepted the charge current without fault flags, and the fuel gauge IC tracked state-of-charge through the full voltage window without triggering a protection cutoff.
• Fuel gauge recalibration after installation: On first use, disable fast charging and run one complete discharge-charge cycle at standard current. The fuel gauge IC on these phones calibrates its coulomb counter against the cell's discharge curve — skipping this step on a new cell leaves the IC reading from the old curve, which causes erratic percentage reporting from day one.

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

This is a voltage cliff issue, not a capacity issue. Under peak modem load or screen-on draw, the new cell's internal resistance causes a voltage dip the BMS reads as a low-cell event, triggering shutdown even when the fuel gauge still shows charge remaining. The RADIANT Core's BMS cutoff threshold sits around 3.4V under load — a new cell with an uncalibrated fuel gauge IC can appear to have 25% remaining while the actual terminal voltage is already at that floor. Run one full discharge to automatic shutdown, then charge uninterrupted to 100% before normal use.

Phone shows wrong battery percentage after replacement

The RADIANT Core uses a fuel gauge IC that tracks cell state by learning the discharge curve of the installed battery over charge cycles. Swap the cell and that learned curve no longer matches the new cell's actual voltage-to-capacity relationship. The result is percentage readings that jump, stall, or report full charge while the phone shuts down minutes later. Fix this by running two complete discharge-charge cycles with the screen brightness low and no fast charge enabled — after two full cycles, the IC resets its reference points against the new cell's actual curve.