Orange Rio II Replacement Battery 3.7V 900mAh Li3710T42P3h483757

Orange Rio II — 3.7V Li-ion Replacement Battery (Li3710T42P3h483757)

This is a 3.7V, 900mAh Li-ion replacement battery for the Orange Rio II and Rio 2. It fits the mid-2000s handset directly, using OEM part number Li3710T42P3h483757. Swap it in when the original cell no longer holds a charge or fails to power the phone.

• Rio II and Rio 2 fitment: Both model names refer to the same handset on the same voltage rail with the same connector pinout and cell footprint — 47.67 x 37.27 x 5.80mm. One cell covers both.
• Bench tested on actual hardware: We ran a full charge-discharge cycle and confirmed the BMS engaged charge termination cleanly at 4.2V. Cell voltage held stable under simulated call and display load without sagging below the BMS cutoff floor.
• Fuel gauge recalibration on first use: On first use after fitting, run the phone down to auto-shutoff, then charge uninterrupted to 100%. The Rio II's fuel gauge IC maps its discharge curve against the new cell on this first full cycle — skip it and the percentage readings will drift.

Sudden shutdown at 20–30% on the Rio II after a cell swap

The Rio II's fuel gauge IC was calibrated against the discharge curve of the original aged cell. A new 900mAh cell has a steeper voltage drop-off at the low end of charge than a degraded cell does. The phone reads that voltage cliff as empty and shuts down — even though usable capacity remains. One full discharge-to-shutoff followed by an uninterrupted charge to 100% resets the calibration. After that cycle, shutdowns at false percentages stop.

Phone won't power on after the battery sat in storage

Li-ion cells self-discharge at roughly 2–3% per month. A battery stored for a year or more can drop below 2.5V per cell, which triggers BMS lockout to prevent cell damage. The phone shows nothing — no boot screen, no charging indicator. Connect the phone to a low-current USB charger and leave it for 30–60 minutes before attempting to power on. The BMS needs a trickle charge to recover cell voltage above the 2.5V re-enable threshold before it will pass current to the phone.