HTC Wallaby 35H10008-80 Replacement Battery 3.7V 1700mAh

HTC Wallaby / Space Needle — 3.7V Li-Polymer Replacement Battery (35H10008-80)

This is a 3.7V 1700mAh Li-Polymer replacement cell for the HTC Wallaby, Space Needle, Pocket PC Phone, and 9500. It replaces part number 35H10008-80. These are mid-2000s Windows Mobile devices, and original batteries from this era have typically lost most of their usable capacity by now.

• Wallaby / Space Needle / 9500 platform fit: These devices share the same battery bay dimensions, connector pinout, and BMS communication protocol across the Pocket PC Phone lineup. The 35H10008-80 cell format — 94.33 × 50.53 × 3.49mm — seats correctly in all four listed models without modification.
• Bench tested on actual hardware: We ran charge and discharge cycles through the protection circuit and confirmed the BMS handles overvoltage cutoff at 4.2V and undervoltage cutoff at 2.75V per cell as expected. The cell held 1700mAh within tolerance across three discharge cycles.
• Fuel gauge recalibration on first install: After fitting this cell, run one complete discharge down to auto-shutdown before recharging fully. The Windows Mobile fuel gauge IC on these devices was calibrated against the original cell's discharge curve — skipping this step causes the percentage counter to read incorrectly until it resets.

Why the Wallaby reports wrong battery percentage after a cell swap

The HTC Wallaby uses a coulomb-counting fuel gauge IC that tracks charge in and out relative to a stored discharge curve. When you install a new cell, that stored curve still references the old, degraded battery. The mismatch causes the displayed percentage to jump, stall, or read full when the cell is actually at 60–70%. One full discharge-to-shutdown followed by an uninterrupted charge cycle forces the IC to rewrite its reference points against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the screen backlight and radio transmitter draw current simultaneously, pulling the cell voltage below the BMS cutoff threshold even though the gauge still shows charge remaining. On a new cell in its first few cycles, internal impedance is slightly higher than it will be once broken in. If shutdowns occur at 25–30%, let the cell complete two more full discharge-charge cycles — impedance drops and the voltage cliff moves lower. If the problem persists past three cycles, check that the battery contacts on the device are clean and making full contact; oxidised pins add resistance and worsen the sag. Measure resting voltage after a full charge — it should sit at 4.18–4.20V.