About this replacement
Telstra R90 Tough / T90 / T6 / T108 — 3.7V Li-ion Replacement Battery (Li3711T42P3h553457)
This is a 3.7V, 1200mAh lithium-ion battery for the Telstra R90 Tough and compatible rugged smartphone models. It replaces OEM part Li3711T42P3h553457. Fit models include the R90 Tough, T90, T6, and T108.
- R90 Tough series compatibility: The R90 Tough, T90, T6, and T108 share the same 3.7V cell format, connector pinout, and BMS handshake protocol — one battery fits all four models without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the R90 Tough platform. The BMS accepted the new cell without a protection lockout event, and charge termination triggered correctly at full voltage.
- Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This gives the fuel gauge IC a clean reference against the new cell's discharge curve before high-current charging begins on an uncalibrated cell.
Sudden shutdown at 20–30% on the R90 Tough after a cell swap
A replacement cell has a slightly different internal impedance profile than the original. Under high-load spikes — LTE modem transmission or screen brightness peaks — the cell voltage sags below the BMS cutoff threshold even when the OS reports 20–30% remaining. The fuel gauge IC is still reading from the old discharge curve it learned on the worn cell. One full uninterrupted discharge-to-charge cycle resets the coulomb counter and maps the new cell's actual voltage-to-capacity curve, eliminating the false cutoff.
USB fast charge not activating after battery replacement
On the first cycle after a cell swap, the R90 Tough's charge IC may not negotiate the fast-charge protocol with the new BMS. This happens because the BMS reports an uncalibrated state of charge, and the charge IC defaults to standard 5V/1A as a safety measure. Complete one full standard charge cycle first. After that cycle, fast charging should handshake correctly on subsequent connections.