Avaya DECT 3740 Replacement Battery 3.7V 1100mAh

Avaya DECT 3740 / DECT 3749 — 3.7V Li-ion Replacement Battery (660273/1B)

This 3.7V, 1100mAh Li-ion battery replaces the original pack in the Avaya DECT 3740, DECT 3749, and 3700 EX cordless phone handsets. It matches OEM part numbers 660273/1B and 1220187. Capacity figure is sourced from the product specification — 4.07Wh total energy.

• DECT 3740, 3749, and 3700 EX compatibility: These three handsets share the same 3.7V single-cell Li-ion platform, identical connector pinout, and the same BMS communication protocol with the base station charge circuit — one pack fits all three.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a DECT 3700-series handset. The BMS accepted the pack immediately, reported correct voltage to the base, and held charge without triggering a fault light.
• First charge after installation: Li-ion cells in DECT handsets ship at a partial state of charge. Seat the handset in the base and leave it for a full charge cycle before taking it off — the base charge circuit needs an uninterrupted session to calibrate to the new cell's capacity curve.

Why the DECT 3740 base station shows a charge fault on a new battery

The DECT 3700-series base reads the incoming cell voltage before it begins charging. If the pack has sat in storage and dropped below roughly 3.0V, the base interprets it as a faulty or absent battery and refuses to start the charge cycle. This is a protection threshold in the base charge IC, not a defect in the battery itself. Remove the handset, hold the power button until the screen clears, then reseat it in the base — this forces the handset's own BMS to wake the cell and present a valid voltage reading. The base should begin charging within 60 seconds.

Handset loses DECT pairing after battery replacement

Pulling the battery cuts all power to the handset's memory, and some DECT 3700-series units drop their base station pairing when that happens. The handset will show "searching" or "no link" on return to power. To re-pair, hold the handset's page or find button and the base's registration button simultaneously until the handset confirms the link — the exact button label varies by site configuration. Once paired, verify the RSSI indicator shows full bars while the handset is within three metres of the base. If it still shows no link, check that the base has not locked its registration slot at maximum capacity.