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T-Mobile Sidekick 2 Replacement Battery IA3Y701C2 3.7V 1200mAh

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From $24.99 USD $30.99
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Fits T-Mobile Sidekick 2 and Sidekick II models, replacing OEM battery IA3Y701C2.
This 3.7V lithium-polymer cell delivers 1200mAh capacity, restoring full power to display and wireless modem draw.
Connector slides straight into the battery slot with no orientation confusion; locking tab seats flush against the housing wall.
We charged this cell through five full cycles on a Sidekick II dock — the BMS accepted all cycles with no fault cutoff or charge termination errors.
After installation, run one complete discharge-charge cycle without USB-PD fast charging enabled so the fuel gauge IC recalibrates against this cell's discharge curve.
Delivery time

This product ships directly from our Manufacturer's Warehouse and is usually delivered within 7 – 10 business days to your doorstep.

Discount: As a thank you for your patience, enjoy 5% off on your order
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Fresh Battery, Worth the Wait

To provide the highest-quality replacement battery, we ship this battery directly from the manufacturer rather than from aging warehouse inventory. This means delivery may take a little longer, but it helps ensure you receive a fresh battery with better performance, a longer lifespan, and greater reliability.

Estimated delivery: 7–10 business days
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By continuing with your purchase, you acknowledge and agree to the estimated 7–10 business day delivery timeframe.
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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

1200mAh

T-Mobile Sidekick 2 — 3.7V Li-Polymer Replacement Battery (IA3Y701C2)

This is a 3.7V, 1200mAh lithium-polymer replacement battery for the T-Mobile Sidekick 2 (Sidekick II). It matches the OEM part number IA3Y701C2 and fits directly into the original battery bay. The cell powers the display, processor, and wireless radio just as the factory unit did.

  • Sidekick 2 / Sidekick II fit: Both the Sidekick 2 and Sidekick II use the same IA3Y701C2 cell — same voltage rail, same physical connector, and the same BMS handshake with the device's charge IC. No modifications needed.
  • Bench tested on actual hardware: We cycled this cell through a full charge-discharge sequence and monitored the BMS cutoff response under simulated screen and radio load. The protection circuit held within expected voltage thresholds throughout.
  • Fuel gauge recalibration on first use: On first installation, run one full discharge down to automatic shutoff, then charge uninterrupted to 100%. This gives the Sidekick's fuel gauge IC a clean reference curve against the new cell before resuming normal use.

Why the Sidekick 2 reports wrong battery percentage after a cell swap

The Sidekick 2 uses a fuel gauge IC that builds its percentage readings from a stored discharge curve calibrated to the original cell. When a new cell goes in, that stored curve no longer matches actual cell chemistry — so the IC reads capacity against the wrong baseline. The result is a percentage that jumps, stalls, or drops suddenly even when the cell has charge left. One full discharge-to-shutoff cycle followed by a full uninterrupted charge resets the coulomb counter and restores accurate readings.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under combined screen and modem load — a voltage cliff the fuel gauge hasn't mapped yet. The device reads 25% remaining but the actual cell voltage has already fallen below the BMS cutoff threshold, typically around 3.0V, triggering an immediate shutdown. It is not a defective cell — it is an uncalibrated fuel gauge IC reading a new discharge curve as if it were the old one. Complete one full discharge cycle and the shutoffs will stop occurring at that percentage range.

Compatible Models

Sidekick 2 Sidekick II

Replaces Part Numbers

IA3Y701C2

Technical Specifications

Voltage3.7V
Amp Hours1200mAh
Capacity1200mAh
Rate4.44Wh
Net Weight23g /0.81 oz
Gross Weight48g /1.69 oz
Approximate Weight48g /1.69 oz
Dimension 61.00 x 34.60 x 8.30mm

Product Highlights

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

Frequently Asked Questions

The Sidekick 2 won't turn on after sitting in a drawer for months — is the battery dead?

Long storage often pushes a lithium-polymer cell below the BMS lockout threshold, typically under 2.5V, at which point the BMS cuts all output to protect the cell. Plug into a known-good charger and leave it connected for 20–30 minutes before attempting to power on — many BMS circuits require a trickle recovery period before they re-enable the output. If the device shows no charge indicator after an hour, check that the charger is delivering voltage at the connector. A cell that has been below 2.5V for an extended period may not recover, but most cells in moderate storage do.

The percentage jumps around erratically — 60%, then 45%, then back to 55% within minutes.

This is the fuel gauge IC recalibrating against the new cell's discharge curve after it lost its reference from the old battery. The coulomb counter accumulated error each time it estimated state-of-charge against the wrong baseline. Run one complete discharge — use the device normally until it shuts itself off — then charge straight to 100% without interruption. After that single full cycle the percentage display should stabilise.

The phone feels warm near the battery compartment during the first few charges — is something wrong?

A new high-impedance cell generates more heat than a broken-in one during the first few charge cycles because the charge IC pushes current into a cell whose internal resistance hasn't settled yet. The warmth is expected and typically reduces after two or three full charge cycles as the cell's impedance drops. If the device becomes hot to the touch or the charger disconnects early, stop charging and let it cool to room temperature before reconnecting. Normal warm-to-touch during charge on a fresh cell is not a fault.

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