I-Mate SP3 Replacement Battery BTR5600B 3.7V 2200mAh

I-Mate SP3 / SP4 Series — 3.7V Li-ion Replacement Battery (BTR5600B)

This is a 3.7V, 2200mAh Li-ion cell for the I-Mate SP3, Spi, SP4, and SP4m smartphones. It fits the original battery bay and connects to the same three-pin contact strip. Capacity is sourced from product data: 2200mAh (8.14Wh).

• SP3 / SP4 platform fit: These models share the same battery footprint, contact pinout, and BMS handshake requirements across the SP3, Spi, SP4, and SP4m. The same cell services all four because Pocket PC Phone Edition and Windows Mobile 5 devices in this line used a common power rail at 3.7V nominal.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on compatible hardware. The BMS accepted charge without triggering overcurrent lockout, and the protection circuit cut off cleanly at the low-voltage threshold rather than allowing deep discharge of the cell.
• Fuel gauge recalibration on first cycle: After installing a new cell, run one full discharge to near shutdown, then charge uninterrupted to 100% before using the device normally. The fuel gauge IC on Windows Mobile-era devices holds the old cell's discharge curve in memory — one full cycle overwrites it and prevents erratic percentage readings from day one.

Why the SP3 reports wrong battery percentage after a cell swap

The SP3 uses a fuel gauge IC that tracks capacity by modelling the discharge curve of the installed cell. When you swap in a new cell, the IC still references the profile it built for the degraded original. A new 2200mAh cell has a steeper, higher voltage curve than a worn cell, so the IC misreads state-of-charge and shows inaccurate percentages. One complete discharge-charge cycle lets the IC rebuild its model against the actual new cell curve. Until that cycle is complete, percentage readings will drift — this is expected behaviour, not a fault with the replacement.

Sudden shutdown at 20–30% remaining on the new cell

This is a voltage cliff issue. Under high-current loads — screen at full brightness, active data sync, or a call — the cell voltage drops sharply. If the fuel gauge IC is still calibrated to the old cell's curve, it predicts remaining capacity incorrectly and the device hits the hardware undervoltage cutoff before the percentage reaches zero. The BMS trips to protect the cell, and the phone shuts down instantly. Run one full discharge cycle to recalibrate the coulomb counter, then check shutdown behaviour. If it persists after two full cycles, confirm the contact strip is seating cleanly and the resting voltage reads at least 3.7V with a multimeter.