HumanWare Touch Replacement Battery 3.7V 5400mAh Li-ion

HumanWare Touch — 3.7V Li-ion Replacement Battery (BAPP-0004)

This is a 3.7V, 5400mAh (19.98Wh) lithium-ion battery for the HumanWare Touch portable note-taking and communication device. The Touch is used by blind and visually impaired users for reading, note-taking, and communication tasks — battery health directly affects access to those functions. This pack matches the OEM part number BAPP-0004 and fits the standard battery bay on the Touch.

• HumanWare Touch compatibility: The Touch uses a single-cell 3.7V Li-ion configuration with a specific BMS handshake tied to the BAPP-0004 part number. Swapping to a non-matched pack can cause the device to misread charge state or refuse to boot entirely.
• Bench tested on actual hardware: We cycled this pack through full charge and discharge on the Touch platform. The BMS communicated correctly with the device, charge acceptance was normal, and no cutoff events triggered during sustained read and audio output sessions.
• First-use initialisation on the Touch: After fitting this pack, charge the device to 100% before powering it on for the first session. The Touch maps battery state on the first full charge cycle — skipping this step causes the charge indicator to display inaccurate percentages during early use.

Why the Touch shuts down during USB data transfer to a PC

When the Touch is connected to a PC for file transfer, the device draws power simultaneously for the USB controller, display, and active storage read/write. A degraded or partially charged cell can't sustain that combined current draw without voltage dropping below the BMS cutoff threshold. This isn't a USB port fault — it's the battery failing to hold voltage under a brief but sharp load spike at transfer start. Charge the battery to full before initiating any PC sync session to avoid this.

Charge indicator jumping erratically after fitting a new pack

New cells come from storage at a partial state of charge, and the Touch's charge reporting is calibrated against a known voltage curve. If the first use begins mid-charge or the device is powered on before a full charge completes, the displayed percentage won't align with actual capacity. The fix is straightforward: charge uninterrupted to 100%, then discharge to below 20% in normal use, and charge again to full. After that cycle, the indicator stabilises and reads accurately — typically showing around 4.2V at full charge.