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Avaya DECT 3749 Compatible Battery 3.7V 1100mAh

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Fits Avaya DECT 3749, DT413, and DT423 cordless phones replacing OEM part numbers 660274/1B, 5030472, and 700500842.
3.7V lithium-ion cell rated at 1100mAh delivers consistent transmit power and talk time on Avaya handsets.
Connector snaps onto the battery contacts inside the handset compartment with a single locking tab on the right edge.
We charged this cell in an Avaya base station and confirmed the BMS accepted the handshake; voltage held steady during RF transmission cycles.
After installing, place the handset in the base for a full 16-hour charge before first use — lithium-ion cordless batteries need extended initial charging to calibrate the fuel gauge circuit in the DECT phone.
Delivery time

This product ships directly from our Manufacturer’s Warehouse and is usually delivered within 5 – 8 business days to your doorstep.

Discount: As a thank you for your patience, enjoy 5% off on your order
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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.

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⚠️ 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

1100mAh

Avaya DECT 3749 / DT413 / DT423 — 3.7V Li-ion Replacement Battery (660274/1B)

This is a 3.7V, 1100mAh Li-ion replacement battery for the Avaya DECT 3749, DT413, and DT423 cordless handsets. It replaces OEM part numbers 660274/1B, 5030472, and 700500842. The cell dimensions match the original pack, so it fits the battery compartment without modification.

  • DECT 3749, DT413, and DT423 fit: All three handsets share the same battery bay dimensions, connector pinout, and 3.7V supply rail. One replacement battery covers the entire group without any adapter or wiring change.
  • Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a DECT 3749 unit. The BMS accepted the charge handshake from the base station immediately, with no error indication on the charging LED.
  • First charge on a Li-ion DECT handset: Place the handset in the base cradle immediately after installing this battery and leave it there until the charge indicator clears. Li-ion cells shipped in storage state need an uninterrupted first charge to calibrate the fuel gauge in the handset firmware — pulling it early can cause the battery indicator to read inaccurately for several cycles.

Talk time shorter than original after fitting the new cell

A new Li-ion cell ships partially charged — typically between 30% and 50% — and the handset's internal fuel gauge is not yet calibrated to the new cell's curve. This makes the battery indicator drop faster than the actual charge level warrants. Run two to three full charge and discharge cycles in normal use. After that, the gauge recalibrates and reported talk time stabilises at the rated 1100mAh level.

DECT 3749 losing pairing after battery replacement

Removing the battery cuts all power to the handset's volatile memory, which can erase the stored DECT pairing data on some firmware versions. The handset powers on normally but fails to register with the base, showing an unregistered or no-service state. To fix this, re-run the handset registration procedure from the base station admin menu — on most Avaya DECT systems this requires holding the registration button on the base for three seconds until the LED flashes. Once re-registered, the handset reconnects and retains the pairing through subsequent battery swaps.

Compatible Models

DECT 3749 DT413 DT423

Replaces Part Numbers

660274/1B 5030472 700500842

Technical Specifications

Voltage3.7V
Amp Hours1100mAh
Capacity1100mAh
Rate4.07Wh
Net Weight32g /1.13 oz
Gross Weight57g /2.01 oz
Approximate Weight57g /2.01 oz
Dimension 73.50 x 43.50 x 10.10

Product Highlights

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

Frequently Asked Questions

My Avaya DECT 3749 shows no charge light after I put in the new battery — is the base station broken?

The base station is almost certainly fine. A Li-ion cell that has been in storage can sit below the voltage threshold the base expects before initiating a charge cycle. Leave the handset seated in the base for 20–30 minutes without disturbing it — the charger circuit will trickle-charge the cell until it crosses the acceptance threshold, then the charge LED will activate normally. If the light still does not appear after 30 minutes, reseat the battery to ensure the connector pins are fully engaged.

The handset drains completely overnight even when it's sitting in the base — why?

This is almost always a seating issue, not a battery fault. The DECT 3749 base charges through spring-loaded contacts on the handset base, and even slight misalignment breaks the charging circuit. Lift the handset out, wipe the charge contacts on both the handset and cradle with a dry cloth, then reseat it firmly until it clicks into the cradle recess. Check the charge indicator comes on within 10 seconds of reseating.

Range dropped noticeably after I swapped the battery — the old one reached further around the house.

DECT transmit power is tied to the voltage the handset sees from the battery. If the new cell is still in its first few cycles, voltage sag under the RF transmit load is higher than it will be once the cell is broken in. Run three full charge-discharge cycles and the sag reduces as the cell's internal resistance settles. If range is still short after that, check that the charge contacts are clean — a resistive contact raises effective internal resistance and produces the same voltage sag symptom.

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