O2 XDA I Replacement Battery 3.7V 1700mAh Li-Polymer

O2 XDA I — 3.7V Li-Polymer Replacement Battery (35H10008-80)

This is a 3.7V, 1700mAh lithium-polymer cell built to the OEM spec for the O2 XDA I smartphone. It replaces part number 35H10008-80 and fits the XDA I directly. The XDA I is a Windows Mobile PDA smartphone from the mid-2000s, and original batteries at this age have typically lost a significant portion of their usable capacity.

• XDA I fit and form factor: The XDA I uses a slim 3.49mm Li-Polymer cell in a fixed bay — this replacement matches those physical dimensions (94.33 x 50.53 x 3.49mm) and the OEM connector pinout. A mismatch here means the battery door won't close or the BMS won't handshake with the charge IC.
• Bench tested on actual hardware: We ran this cell through the XDA I charge cycle and confirmed the BMS communicates correctly with the device's charge controller. Charge termination triggered cleanly at full capacity without false cutoffs.
• Fuel gauge recalibration on first use: On first installation, let the battery run down to automatic shutdown, then charge uninterrupted to 100%. The XDA I's fuel gauge IC was calibrated against the old cell's degraded curve — one full discharge-charge cycle resets it against the new cell.

Why the XDA I reports wrong battery percentage after a cell swap

The XDA I tracks charge state using a fuel gauge IC that builds its model from the previous cell's discharge curve. When you install a new cell with a different internal impedance profile, that model is stale. The gauge reads voltage and compares it against the old curve, so it reports inaccurate percentages — often showing full charge dropping rapidly or stalling at a fixed number. One complete discharge-to-shutdown followed by a full uninterrupted charge forces the IC to relearn the new cell's characteristics.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC hasn't recalibrated yet and the reported percentage doesn't reflect actual cell voltage. Under load — screen backlight, radio, or data sync running simultaneously — the cell voltage drops sharply at a point the old curve didn't anticipate. The device interprets this as a hard undervoltage condition and cuts power to protect the cell. Run one full discharge cycle without interruption, then charge to 100%. After that cycle, shutdown-under-load events at 20–30% typically stop.