ZTE S2x Replacement Battery Li3710T42P3h553457 3.7V 800mAh

3 Skype S2x — 3.7V Li-ion Replacement Battery (Li3710T42P3h553457)

This is a 3.7V 800mAh Li-ion replacement battery for the 3 Skype S2x smartphone. It matches the OEM part number Li3710T42P3h553457 and fits directly into the S2x battery bay. Use it when the original cell no longer holds a charge or fails to power the device reliably.

• S2x battery bay fit: The S2x uses a compact 54.54 x 33.69 x 5.26mm cell with a low 3.7V nominal rail. This replacement matches those physical and electrical specs exactly — the connector orientation and BMS communication pins align with the S2x charge IC without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS held cutoff correctly at both the low-voltage floor and the 4.2V charge ceiling. No thermal events. Charge IC handshake completed on the first connection.
• Fuel gauge recalibration on first cycle: On first use after installation, run the phone down to automatic shutdown, then charge uninterrupted to 100% before using it. This gives the fuel gauge IC one complete reference cycle against the new cell's discharge curve before the OS starts reading percentage.

Why the S2x reports wrong battery percentage after a cell swap

The S2x uses a fuel gauge IC that builds its percentage model from the discharge curve of the cell it was calibrated against — the original factory cell. A new cell has a slightly different impedance and discharge curve, so the IC's stored model is mismatched from the first charge. The OS reads from that IC, so it reports whatever the IC calculates, not what the cell is actually doing. One full discharge-charge cycle writes a new reference point into the coulomb counter and closes the gap. After that cycle, percentage accuracy returns to normal.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops below the modem or display load threshold before the fuel gauge IC expects it to. A fresh cell sometimes has a steeper voltage cliff in the lower charge range than the IC's stored curve predicts, so the phone cuts out at what still looks like 20–30% remaining. It is not a faulty cell — it is the IC recalibrating. Let the phone shut down on its own, charge it fully without interruption, and repeat once more. After two full cycles the coulomb counter re-maps the low-end voltage behaviour and shutdowns stop occurring above 10%.