About this replacement
T-Mobile MDA Vario IV — 3.7V Li-ion Replacement Battery (DIAM171)
This is a 3.7V, 2700mAh Li-ion battery for the T-Mobile MDA Vario IV Windows Mobile PDA. It replaces OEM part numbers DIAM171, 35H00111-08M, and 35H00111-06M. If the original cell no longer holds charge or drops voltage unexpectedly, this is the direct swap.
- MDA Vario IV compatibility: The Vario IV uses a standard single-cell Li-ion pack at 3.7V nominal. The BMS in this unit monitors cell voltage and temperature — this replacement battery communicates correctly with that circuit without triggering low-voltage lockout on boot.
- Bench tested on actual hardware: We cycled this battery through charge and discharge on the MDA Vario IV platform. The BMS handshake completed normally, charge acceptance was consistent, and the device did not report battery errors in the system tray.
- Sync before you swap: The MDA Vario IV stores open application state and unsaved data in RAM, which is powered directly by the main battery. Pull a full ActiveSync or Windows Mobile Device Center sync to your host PC before removing the old cell — anything not synced will be lost the moment power cuts.
Why the MDA Vario IV loses saved data when the battery is removed
The Vario IV uses SRAM for active storage, and that memory requires constant voltage to retain data. Unlike flash-based storage, SRAM clears the moment the battery is disconnected — even briefly. Contacts, calendar entries, and app data written to RAM disappear on a full power cut. To protect that data, always sync to a host computer before swapping the battery, and confirm the sync completed before removing the cell.
MDA Vario IV stuck on boot screen after new battery installation
A freshly shipped Li-ion cell often sits at 30–50% charge from storage, which can fall below the minimum voltage the Vario IV's boot sequence requires. The device stalls at the boot logo because the system checks cell voltage before handing off to the OS. Connect the device to a charger and let it charge for at least 30 minutes before attempting to power on. Once the battery reaches approximately 3.6V, the boot sequence should complete normally.