Unify OpenStage SL4 Replacement Battery 3.7V 950mAh

Unify OpenStage SL4 / OpenScape SL5 — 3.7V Li-ion Replacement Battery

This 3.7V, 950mAh lithium-ion battery replaces the original cell in the Unify OpenStage SL4, OpenStage SL4 professional, OpenScape SL5 professional, and related cordless DECT handsets. It restores power to handsets that no longer hold a charge or fail to complete a full day of use. Dimensions are 52.95 × 35.10 × 4.50mm — confirm against your existing cell before installing.

• OpenStage SL4 and SL5 platform fit: These handsets share the same battery bay dimensions and 3.7V supply rail across the SL4, SL4 professional, and SL5 professional variants. One cell covers the full range listed in the compatibility data.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the SL4 platform. The protection circuit responded correctly to low-voltage cutoff and did not trip during normal DECT transmit bursts.
• First-charge protocol for DECT handsets: After fitting, seat the handset in its base station and leave it undisturbed for a full 16 hours before first use. Li-ion cells shipped in storage state need a complete slow charge to reach rated capacity — pulling the handset off the base early leaves usable charge on the table.

Talk time shorter than expected after fitting a new cell

A freshly installed Li-ion cell often delivers noticeably less talk time for the first two or three charge cycles. This happens because the cell ships in a partially discharged storage state, and the handset's charge management circuit calibrates to actual capacity over repeated full cycles. Run three complete charge-and-use cycles before judging performance. By cycle three, the cell should be delivering close to its rated 950mAh.

Handset fails to re-pair with base station after battery replacement

Removing the battery completely cuts power to the handset's volatile memory, and some DECT implementations lose their pairing registration when that happens. The base station treats the handset as an unknown device on next power-up. To fix this, initiate a fresh DECT registration from the base station menu — on most Unify bases, this is found under Settings → Registration → Register Handset. Once re-paired, the handset functions normally.