About this replacement
Avaya 3631 / SMT-W5110 — 3.7V Li-ion Replacement Battery (700431489)
This is a 3.7V Li-ion battery rated at 1100mAh (4.07Wh) for the Avaya 3631 cordless DECT handset and the SMT-W5110 series. It replaces OEM part numbers 700431489 and 700431497. Install it when the original cell no longer holds a charge or the handset shuts off before the end of a call.
- 3631 and SMT-W5110 platform fit: Both the 3631 Comcode and SMT-W5110C variants use the same 3.7V single-cell Li-ion pack with an identical connector footprint and BMS handshake profile, so one cell covers all four models listed.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on a 3631 handset and confirmed the BMS accepted the pack without fault codes, held the voltage rail steady under active call load, and terminated charge cleanly at 4.2V.
- First charge on a Li-ion DECT handset: After fitting this cell, seat the handset in the base cradle and leave it for a full uninterrupted charge cycle before use — Li-ion packs shipped at storage charge need one complete fill to let the BMS calibrate the state-of-charge register accurately.
Talk time shorter than expected after replacing the 3631 battery
A new Li-ion cell arrives at roughly 40–60% charge from storage. If you use the handset before the first full charge cycle completes, the BMS reads an inaccurate capacity baseline and may cut off early. This is not a faulty cell — it is the BMS working from incomplete calibration data. Seat the handset in the base, let it charge without interruption, then run it through two full charge-discharge cycles. Talk time will reach rated capacity by the third cycle.
Avaya 3631 handset loses DECT pairing after battery swap
Removing the battery on some DECT handsets clears the volatile memory that stores the base station pairing record. The handset powers on but shows no signal or fails to register. This is not a battery fault — it is a firmware behaviour triggered by total power loss. Re-register the handset from the base station menu using the same subscription PIN used during initial setup, typically four zeros by default on Avaya systems.