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T-Mobile MDA Vario IV Compatible Battery DIAM171 3.7V 2700mAh

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From $28.99 USD $35.99
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Fits T-Mobile MDA Vario IV; replaces DIAM171, 35H00111-08M, 35H00111-06M battery packs.
3.7V, 2700mAh lithium-ion cell restores full power capacity to aging Vario IV units.
Connector slides straight into the factory slot; locking tab secures flush against the device.
We bench-tested this cell in a Vario IV unit — BMS accepted the pack on first insertion, no contact cleaning required.
Sync all open files and calendar data to your desktop computer before removing the old battery; the Vario IV powers RAM from the main pack, and full power loss erases unsaved application state.
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Battery Care Tips

🔹 Getting Started

Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.

🔹 Keep It Healthy

Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.

Delivery and Shipping

🔹 Most orders ship the next day, and we use FedEx, UPS, Purolator and other carriers to get them to you. Lithium batteries have to ship by ground only, not air or USPS. Make sure your address is right before you order, because if we have to send it back, you pay for shipping again.

Disclaimer

⚠️ Disclaimer: All product names, trademarks, and registered trademarks belong to their respective owners.

🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.

Voltage

3.7V

Amp

2700mAh

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.

Compatible Models

MDA Vario IV

Replaces Part Numbers

DIAM171 35H00111-08M 35H00111-06M

Technical Specifications

Voltage3.7V
Amp Hours2700mAh
Capacity2700mAh
Rate9.99Wh
Gross Weight100g /3.53 oz
Approximate Weight100g /3.53 oz

Product Highlights

  • Brand: T-Mobile
  • Manufacturer: CS
  • Series: Standard
  • Color: Metallic Grey
  • Product Type: Li-ion
  • Battery Type: Li-ion
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My MDA Vario IV lost all my contacts and calendar after I swapped the battery — is that normal?

Yes, and it happens because the Vario IV stores active data in SRAM, which needs continuous power to hold its contents. The moment the old battery is removed, that memory clears — there is no backup cell buffering it. To prevent this on your next swap, run a full ActiveSync or Windows Mobile Device Center sync to your PC before touching the battery, and confirm all items transferred before disconnecting.

The MDA Vario IV won't boot after fitting the new battery — it just sits on the logo screen.

The Vario IV checks cell voltage early in the boot sequence, and a new battery shipped at partial charge can fall below that threshold. Connect to a charger via USB or the wall adapter before you try to power on. Let it charge for at least 30 minutes, then attempt boot — the device should progress past the logo once the cell reaches around 3.6V.

Wi-Fi on my MDA Vario IV keeps dropping or won't connect properly since fitting the new battery — what's causing that?

The Vario IV's wireless radio is voltage-sensitive and draws a short, sharp current spike when it initialises. If the battery is not at a full charge when you first attempt a Wi-Fi connection, voltage can sag enough to cause the radio to drop or fail to associate. Charge the device fully before running wireless sync or browsing — confirm the battery indicator shows a full charge in the system tray before enabling the radio.

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