Avaya INDEX DT20 Replacement Battery 3.6V 700mAh

Avaya INDEX DT20 / WT9620 Series — 3.6V Ni-MH Replacement Battery (NT7B65KSE6)

This is a 3.6V, 700mAh Ni-MH replacement battery for the Avaya INDEX DT20, 20DT, WT9620, and 7420 cordless DECT handsets. It replaces OEM part numbers NT7B65KSE6, NTTQ47KAE6, NT7B80BXE6, NT7B65LDE6, and NT7B65LD. When the original cell degrades and the handset spends more time on the base than off it, this cell restores full talk time and standby operation.

• INDEX DT20 and WT9620 platform compatibility: These models share the same 3.6V single-cell NiMH rail, identical connector pinout, and matching physical footprint — 45.00 × 31.10 × 10.50mm. The base station's charging circuit expects a NiMH profile on that voltage rail, so chemistry match matters here.
• Bench tested on actual hardware: We cycled this cell through the Avaya base station charging circuit and confirmed the BMS accepted the pack without error flags. Charge acceptance, termination, and trickle behaviour all matched factory cell behaviour across three consecutive cycles.
• First-charge protocol for NiMH cordless handsets: After installing, seat the handset in the base and leave it for a full 16 hours before first use. NiMH cells shipped in partial-discharge state need this slow initial charge to reach rated capacity — skipping it leaves capacity permanently suppressed on this platform.

Talk time shorter than original battery after replacement

NiMH cells take three to five full charge-discharge cycles to reach their rated 700mAh capacity. On the first cycle, effective capacity may read as low as 60–70% of rated. This is not a fault — it is electrochemical conditioning, and it is normal for this chemistry on DECT handsets. Run three complete cycles in the Avaya base before judging talk time.

Base station showing no charge or error light after new pack installed

NiMH cells stored in a warehouse drop to low resting voltages over time. The Avaya base station charging circuit has a minimum acceptance threshold — if the incoming cell voltage is too low, the base flags an error rather than starting a charge. Remove the handset, leave the battery installed, and place the handset back in the base for 30 minutes. The trickle pre-charge stage should bring the cell above the acceptance threshold and allow normal charging to resume at 3.6V nominal.