Avaya MM588 Cordless Phone Replacement Battery 3.7V 950mAh

Avaya MM588 — 3.7V Li-ion Replacement Battery (4.998.020.274)

This is a 3.7V, 950mAh Li-ion replacement battery for the Avaya MM588 cordless DECT handset. It replaces OEM part 4.998.020.274. Fit it when the original no longer holds a charge or the handset dies faster than it used to.

• MM588 handset compatibility: The MM588 runs a single-cell 3.7V Li-ion pack with a specific connector orientation and cell footprint. This battery matches those physical and electrical specs — same cell dimensions (61.28 × 50.19 × 10.21mm), same nominal voltage, same BMS communication the handset expects.
• Bench tested on actual hardware: We cycled this battery through charge and discharge on the MM588 platform. The BMS held the charge threshold correctly and the handset recognised the pack without showing a fault indicator on the base station.
• First-charge protocol for the MM588: After fitting, seat the handset in the base and leave it for a full charge cycle without interruption. Li-ion cells shipped at partial state of charge need one complete cycle to calibrate the handset's charge indicator to the new pack's actual capacity.

Talk time shorter than expected after replacing the MM588 battery

A new Li-ion cell ships at around 40–60% state of charge. If you start using the handset before the battery reaches full charge, the handset's fuel gauge calibrates against that partial capacity and reads short from that point forward. One full uninterrupted charge cycle from near-empty to full resets the calibration. After that, the handset's battery indicator should track accurately against the 950mAh rated capacity.

Handset not pairing with the base after battery swap

Removing the battery from a DECT handset cuts all power to the radio module, which can wipe the pairing data stored in volatile memory. The MM588 handset may show no signal or fail to register on the base after a cold swap. To fix this, re-register the handset from the base station menu — typically found under system or handset settings. Once registration completes, the handset resumes normal DECT operation.