Telstra F158 Li-ion Replacement Battery 3.7V 1700mAh

Telstra F158 / F159 / X185 — 3.7V Li-ion Replacement Battery (Li3717T42P3h5637116)

This is a 3.7V, 1700mAh Li-ion cell built to fit the Telstra F158, F159, and X185 smartphones. It replaces OEM part number Li3717T42P3h5637116 directly. If your original cell no longer holds charge through a normal day, this is the replacement cell for that slot.

• F158, F159, and X185 share this cell: All three models run the same 3.7V battery rail, use the same physical connector, and accept the same BMS handshake — which is why one part number covers the entire group.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS engaged correctly at both the low-voltage cutoff and the full-charge termination point. No false trips or charge interruptions were recorded during testing.
• Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging begins on an uncalibrated cell.

Why the F158 reports wrong battery percentage after a cell swap

The F158 uses a fuel gauge IC that builds its percentage model from the previous cell's discharge history. When you swap in a new cell, that stored model no longer matches the actual discharge curve of the replacement. The phone reads voltage and translates it to percentage using old data, so the numbers are wrong until the IC relearns. One full discharge from 100% down to auto-shutdown, followed by a full uninterrupted charge to 100%, resets the coulomb counter and lets the gauge IC recalibrate against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff issue. Under peak modem or screen load, the cell voltage drops sharply — faster than the fuel gauge IC predicted — and the BMS trips the output before the displayed percentage reaches zero. It looks like a random shutdown, but it is the BMS responding correctly to a voltage that fell below the cutoff threshold. The fix is the same recalibration cycle: run the phone down to auto-shutdown rather than plugging in early. After one or two full cycles, the gauge IC tracks the actual voltage curve and the shutdowns stop.