AT&T Cingular Flex HE402 Replacement Battery 3.7V 1100mAh
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AT&T Cingular Flex HE402 Replacement Battery 3.7V 1100mAh - is backordered and will ship as soon as it is back in stock.
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Battery Care Tips
Battery Care Tips
🔹 Getting Started
Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.
🔹 Keep It Healthy
Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.
Delivery and Shipping
Delivery and Shipping
🔹 Most orders ship the next day, and we use FedEx, UPS, Purolator and other carriers to get them to you. Lithium batteries have to ship by ground only, not air or USPS. Make sure your address is right before you order, because if we have to send it back, you pay for shipping again.
Disclaimer
Disclaimer
⚠️ Disclaimer: All product names, trademarks, and registered trademarks belong to their respective owners.
🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.
AT&T Cingular Flex HE402 Replacement Battery 3.7V 1100mAh - is backordered and will ship as soon as it is back in stock.
Voltage
3.7V
Amp
1100mAh
AT&T Cingular Flex / Flex 4G LTE Flip — 3.7V Li-ion Replacement Battery (HE402)
This 3.7V, 1100mAh Li-ion cell replaces the OEM HE402 battery in the AT&T Cingular Flex and Flex 4G LTE Flip (ATTEA211101). It restores power to the phone's cellular modem, display, and onboard computing. Capacity is rated at 4.07Wh — identical to the original specification.
- Cingular Flex and Flex 4G LTE Flip compatibility: Both models use the same HE402 cell format, voltage rail, and connector pinout. The BMS handshake and charge termination voltage are matched to the AT&T charging firmware on these devices.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the Flex platform. The BMS held cutoff correctly at low voltage and accepted charge termination without triggering error flags on the device.
- 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 the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell.
Sudden shutdown at 20–30% on the Cingular Flex after a cell swap
The Cingular Flex draws a sharp current spike when the modem transmits or the screen refreshes at full brightness. A new cell with slightly higher internal impedance than the aged original can drop below the BMS cutoff voltage under that load — even when the fuel gauge still reads 20–30%. This is a voltage cliff, not a capacity problem. One full discharge-to-cutoff followed by a complete charge cycle lets the coulomb counter recalibrate and the shutdowns stop.
OS reporting incorrect battery percentage after replacement
The fuel gauge IC stores a learned discharge curve from the old cell. When a new cell goes in, the IC applies the old curve to new voltage readings — producing percentages that jump or read high before dropping fast. This is not a fault with the replacement cell. Run one full discharge down to automatic shutdown, then charge uninterrupted to 100% without using the device. After that cycle, the IC recalculates against the actual cell curve and percentage reporting stabilises.
Compatible Models
Replaces Part Numbers
Technical Specifications
Product Highlights
- Brand: AT&T
- Manufacturer: CS
- Series: Standard
- Color: Black
- Product Type: Li-ion
- Battery Type: Li-ion
- Warranty: 12 Months
- Bulk Orders: sales@batteryweb.com
Frequently Asked Questions
My AT&T Cingular Flex shut off at 25% right after I put the new battery in — is the replacement dead?
It is not dead. A new cell has higher internal impedance than a worn original, so when the modem fires or the screen peaks, voltage drops sharply below the BMS cutoff even though the gauge still shows charge remaining. This is a voltage cliff caused by the fuel gauge IC using the old cell's discharge curve. Run one full discharge to automatic shutdown, then charge to 100% without interruption — the coulomb counter recalibrates and the shutdowns stop.
The Cingular Flex won't fast charge after I installed the replacement — it only trickle charges on the first plug-in.
On the first connection after a cell swap, the charge IC on the Flex defaults to a low-current pre-charge mode while it verifies the new cell's voltage and BMS response. This is normal behaviour, not a fault. Let the first charge run to 100% at whatever rate the device selects. On subsequent cycles, the charge IC accepts the higher current rate and fast charging resumes — typically after one complete charge.
The replacement battery was in storage and the Cingular Flex won't turn on at all now — screen stays black.
If the cell discharged below approximately 2.5V during storage, the BMS enters lockout to prevent damage to a deeply discharged lithium cell. Plug the phone into the OEM charger and leave it connected for 20–30 minutes without pressing any buttons — the charge IC applies a recovery trickle current to bring the cell back above the BMS re-enable threshold. Once voltage crosses that threshold, the phone boots normally. If the screen shows nothing after 45 minutes on charge, check that the battery connector is fully seated.
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