Cingular Flex HE402 Replacement Battery 3.7V 1100mAh

Cingular Flex / Flex 4G LTE Flip — 3.7V Li-ion Replacement Battery (HE402)

This is a 3.7V, 1100mAh Li-ion replacement battery for the Cingular Flex and Flex 4G LTE Flip smartphones. It carries OEM part numbers HE402 and BPACD00001B and fits the ATTEA211101 variant as well. Install it when the original cell can no longer hold enough charge to keep the phone operational through a normal day of calls and messaging.

• Flex and Flex 4G LTE Flip compatibility: Both handsets share the same battery bay dimensions, connector pinout, and BMS handshake protocol — a single cell covers both. The 53.40 × 38.00 × 5.50mm footprint seats flush without modification.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the Flex platform. The BMS accepted charge correctly, reported state-of-charge without error flags, and held rail voltage stable under simultaneous screen and modem load.
• Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging and complete one full discharge-to-charge cycle. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging pushes current into an uncalibrated register — preventing erratic percentage readings from the first session.

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

A fresh cell does not automatically inherit the fuel gauge IC's learned discharge curve from the old battery. When the Flex's modem fires a high-current burst — during a call or a data sync — the new cell may drop below the shutdown threshold momentarily even though the reported percentage looks safe. The phone cuts power to protect itself. One complete, uninterrupted discharge-to-charge cycle without fast charging resets the coulomb counter and aligns the gauge to the actual cell curve. After that cycle, shutdowns at mid-percentage typically stop.

Phone warm near the battery compartment on the first few charges

A new cell arrives with higher internal impedance than a broken-in one. The charge IC pushes its standard current profile into that resistance, and the extra energy dissipates as heat at the battery. This is normal for the first two to three charge cycles as the cell's internal resistance settles. If the phone remains warm beyond the fifth charge or the battery compartment becomes hot to the touch, check that the charge IC is not stuck in a fast-charge mode — drop to a standard 5V/1A charger and monitor surface temperature on the next cycle.