HB5K1H AT&T U8652 Replacement Battery 3.7V 1200mAh

AT&T U8652 Fusion MF / Jengu — 3.7V Li-ion Replacement Battery (HB5K1H)

This is a 3.7V, 1200mAh Li-ion cell built to the HB5K1H specification. It fits the AT&T U8652 Fusion MF, U8652 Jengu, and U8652 Fusion variants. Slide it into the battery bay and the phone's charge IC picks it up immediately.

• U8652 series compatibility: The Fusion MF, Jengu, and standard U8652 all use the same battery bay dimensions, connector pinout, and 3.7V nominal rail. One cell covers the full lineup because the BMS handshake is identical across these variants — no firmware differences affect charging acceptance.
• Bench tested on actual hardware: We cycled this cell through charge, standby, and active modem load on the U8652 platform. The charge IC accepted the cell on the first connection, the BMS reported state-of-charge correctly after one full discharge-charge cycle, and no cutoff events occurred under sustained data and call load.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging and run one complete discharge-charge cycle before normal use. The fuel gauge IC on the U8652 is calibrated to the old cell's discharge curve — giving it one full uninterrupted cycle lets it map the new cell's voltage curve accurately before you rely on the percentage reading.

Sudden shutdown at 20–30% on the U8652 after a cell swap

This happens because the fuel gauge IC still holds the discharge curve of the degraded original cell. When the new cell's actual voltage drops under modem or screen load, the reported percentage and the real voltage no longer match — the phone hits a hardware voltage floor and cuts out before the gauge reads zero. The fix is a full recalibration cycle: charge to 100%, let the phone run down to automatic shutdown without interruption, then charge back to 100% in one go. After that cycle the coulomb counter resets to the new cell's curve and the shutdowns stop.

Battery percentage jumping erratically after installation

Erratic percentage readings — jumping from 60% to 40% or spiking briefly — are a fuel gauge IC artefact, not a cell defect. The IC accumulated offset errors tracking the old cell's degraded capacity and is now applying those errors to a fresh cell with a different internal resistance profile. Run two consecutive full discharge-charge cycles with the screen on and mobile data active to keep the load consistent. After the second cycle the coulomb counter stabilises and percentage readings track smoothly.