Avaya 4027 Cordless Phone Compatible Battery 3.7V 1200mAh

Avaya 4027 / 4070 Series — 3.7V Li-ion Replacement Battery

This 3.7V, 1200mAh Li-ion battery replaces the original pack in the Avaya 4027 and 4070 DECT cordless handsets, including units listed under part numbers NTTQ81EAE6 and NTTQ82EAE6. It slots into the battery compartment using the same form factor as the stock cell — 53.20 x 34.00 x 5.70mm. If your handset has been cutting out early or refusing to hold a charge, this is the direct swap.

• 4027 and 4070 platform fit: Both models share the same battery bay dimensions and 3.7V supply rail. The connector orientation and cell footprint are identical across the NTTQ81EAE6 and NTTQ82EAE6 variants, so one battery serves the full lineup without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the 4027 handset. The onboard protection circuit handled over-voltage cutoff cleanly and the base station registered a full charge cycle without error flags.
• First charge on DECT Li-ion handsets: After fitting this battery, seat the handset in the base cradle and leave it for a full charge before first use. Li-ion cells shipped in partial-charge storage state need one complete charge cycle to allow the handset's fuel gauge to calibrate correctly — skipping this causes the battery indicator to read inaccurately from day one.

Why the 4027 handset loses range shortly after a battery swap

DECT transmit power draws current in short bursts. When a Li-ion cell is low on charge or hasn't completed its first calibration cycle, voltage sags during those RF bursts. The handset's radio drops to a lower power mode to compensate. Range shrinks noticeably even though the battery indicator still shows partial charge. A full charge cycle resolves this — the cell stabilises above 3.6V under transmit load.

Handset not pairing with the base after battery replacement

Removing the battery cuts all power to the handset, including the memory that stores DECT pairing data on some 4027 units. The base station and handset lose each other after a full power-off. To fix this, re-register the handset through the base station's subscription mode — typically held via the locator button on the base for five seconds. Check the handset display for a "searching" or "no link" message first to confirm pairing is the actual fault before assuming a hardware issue.