AT&T Phoenix 3.7V Replacement Battery 1500mAh Li-ion

AT&T Phoenix P505 — 3.7V Li-ion Replacement Battery

This 3.7V, 1500mAh Li-ion battery replaces the original cell in the AT&T Phoenix (P505) smartphone. It fits directly into the Phoenix's battery bay and restores the phone to normal operation when the original cell has degraded past usable capacity. Dimensions are 65.00 × 43.50 × 5.00mm — confirm these against your existing battery before installing.

• Phoenix P505 fitment: The P505 uses a single-cell Li-ion pack at 3.7V nominal. The charge IC and fuel gauge IC on the Phoenix mainboard communicate directly with the battery's BMS — voltage rail and physical connector must match the OEM spec for the phone to boot and charge correctly.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Phoenix platform. The BMS held cutoff at the correct lower voltage threshold, and the charge IC accepted the cell without throwing a charge-fault error.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging begins on an uncalibrated cell.

Sudden shutdown at 20–30% on the replacement cell

The Phoenix's fuel gauge IC was calibrated to the discharge curve of the original, degraded cell. When a fresh cell with a steeper voltage cliff near depletion is installed, the gauge misreads state of charge. The phone cuts power when actual cell voltage drops below the modem and display load threshold — even though the reported percentage still reads 20–30%. One full uninterrupted discharge-charge cycle resets the coulomb counter and brings the gauge back into alignment with the new cell's curve.

Phone warm near the battery during the first few charges

A new Li-ion cell has higher internal impedance than a broken-in cell. The charge IC on the Phoenix pushes current into that higher impedance, and the cell dissipates some energy as heat during the first few cycles. This is normal and tapers off as the cell breaks in over two to three full cycles. If the phone becomes hot to the touch — not just warm — remove it from the charger and check that the battery is seated flat with no gap at the connector.