Telstra F252 Li3707T42P3h513651 Compatible Battery 3.7V 700mAh

Telstra F252 / F850 Series — 3.7V Li-ion Replacement Battery (Li3707T42P3h513651)

This is a 3.7V 700mAh Li-ion cell built to the OEM spec for the Telstra F252, F256, F850, and F851 mobile phones. It matches the original part number Li3707T42P3h513651 and fits the same battery bay without modification. Capacity is 700mAh (2.59Wh), identical to the factory cell.

• F252, F256, F850, F851 compatibility: These four handsets share the same battery bay dimensions (50.38 × 35.21 × 5.01mm), connector pinout, and BMS handshake protocol — which is why a single cell covers the full range.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on an F850 unit. The BMS accepted the cell without error flags, and charge termination triggered correctly at 4.2V. Voltage under screen-on load held steady with no unexpected cutoff.
• Fuel gauge recalibration on first use: On first installation, disable fast charging if your charger supports it and run one complete discharge-charge cycle at standard current. This gives the phone's fuel gauge IC time to map the new cell's discharge curve before high-current charging begins against an uncalibrated counter.

Sudden shutdown at 20–30% on the F252 and F850

This happens when a degraded cell can no longer sustain voltage under the load spikes from the modem radio or screen backlight. Even though the fuel gauge still reads 20–30%, the cell voltage collapses below the BMS cutoff threshold — typically around 3.0V — and the phone shuts off instantly. A fresh cell with lower internal resistance holds voltage through those load spikes. After fitting this replacement, one full discharge-charge cycle will let the fuel gauge IC recalibrate and eliminate the early-shutdown readings.

Phone reports wrong percentage after cell swap

The F252 and F850 use a fuel gauge IC that tracks charge using a coulomb counter calibrated to the old cell's discharge curve. When you fit a new cell, the stored curve no longer matches, so the percentage display jumps or reads incorrectly. The fix is straightforward: run the phone down until it powers off on its own, then charge uninterrupted to 100% without removing the charger early. After one complete cycle, the fuel gauge IC resets its reference points against the new cell and percentage readings stabilise.