SRF StarTrail 2 Replacement Battery 3.7V 1200mAh Li-ion

SRF StarTrail 2 — 3.7V Li-ion 1200mAh Replacement Battery

This is a 3.7V Li-ion cell rated at 1200mAh (4.44Wh), sized as a direct physical fit for the SRF StarTrail 2 smartphone. It replaces a degraded or failed original cell that can no longer hold a usable charge. Dimensions are 49.50 × 44.20 × 4.50mm — confirm against your existing cell before fitting.

• StarTrail 2 cell compatibility: The StarTrail 2 uses a compact 3.7V single-cell configuration with a low-current BMS that matches this cell's charge termination voltage and protection thresholds. Swapping in a mismatched cell chemistry or higher voltage can trip the charge IC permanently.
• Bench tested on actual hardware: We cycled this cell through charge and discharge under screen-on and modem-active loads. The BMS held protection thresholds correctly and charge termination occurred at the expected 4.2V cutoff without anomalies.
• 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 recalibrate against the new cell's discharge curve before high-current charging pushes current into an uncalibrated state.

Why the StarTrail 2 reports wrong battery percentage after a cell swap

The StarTrail 2 uses a coulomb-counting fuel gauge IC that builds its reference model from the original cell's discharge curve. When a new cell goes in, that stored model no longer matches actual cell behaviour. The IC will show inflated or deflated percentages until it completes at least one full charge-to-discharge cycle. Run the phone from 100% down to automatic shutdown, then charge uninterrupted to 100% — one complete cycle resets the reference model.

Sudden shutdown at 20–30% charge remaining on the replacement cell

This happens when the cell voltage drops sharply under load — typically during screen brightness peaks or mobile data bursts — faster than the fuel gauge IC predicted from its uncalibrated model. The phone's low-voltage protection trips before the displayed percentage reaches zero. It is not a faulty cell. Complete one full calibration cycle as described above, and the IC will map the new cell's actual voltage cliff and adjust shutdown timing to match real remaining capacity.