Telstra 4GX HD Replacement Battery 3.8V 2200mAh

Telstra 4GX HD — 3.8V Li-ion 2200mAh Replacement Battery

This 3.8V Li-ion cell delivers 2200mAh (8.36Wh) to the Telstra 4GX HD smartphone. It fits the internal battery bay directly, matching the original cell's voltage rail and connector. No OEM part number exists for this battery; fitment is confirmed by model and physical dimensions (74.00 × 62.14 × 4.10mm).

• 4GX HD fitment: The 4GX HD runs a single-cell Li-ion architecture at 3.8V nominal. This replacement matches that voltage rail and the physical envelope — thickness is fixed at 4.10mm, which is the critical dimension inside the rear housing stack.
• Bench tested on actual hardware: We cycled this cell through a full charge and discharge sequence, monitoring BMS cutoff at the low-voltage threshold. The protection circuit tripped correctly at the expected floor and accepted a standard 5V charge input without fault flags.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle. The fuel gauge IC in the 4GX HD is calibrated to the old cell's discharge curve — letting it recalibrate against the new cell before high-current charging resumes prevents erratic percentage readings from the start.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff issue, not a capacity fault. Under peak load — LTE modem transmit, screen at full brightness, or GPS active — the new cell's internal resistance causes a momentary voltage sag. The phone's power IC reads that sag as a critical low-voltage event and cuts the system before the reported percentage reaches zero. The fuel gauge IC hasn't yet mapped the new cell's actual discharge curve, so the displayed percentage is inaccurate at high draw. Run two full discharge-charge cycles without fast charging to let the coulomb counter recalibrate, then test again at full load.

Phone won't power on after the battery sat discharged in storage

If the cell dropped below approximately 2.5V while stored, the BMS enters a lockout state to prevent charging a deeply discharged lithium cell. The phone will show no response — no boot, no charging indicator. Connect to a 5V USB source and leave it for 15–20 minutes without pressing the power button; the BMS uses a trickle pre-charge path to recover the cell voltage back above the lockout threshold. Once the cell climbs above roughly 3.0V, the BMS re-enables normal charge current and the charging indicator will appear. If no response after 30 minutes on USB, the cell voltage may be below recoverable range.