OpenStage SL4 Compatible Battery 3.7V 950mAh Li-ion

OpenStage SL4 / SL5 / SL6 — 3.7V Li-ion Replacement Battery

This 3.7V, 950mAh Li-ion battery fits the OpenStage SL4, SL5, and SL6 DECT cordless handsets. It replaces the original cell when talk and standby time drop noticeably after repeated charge cycles. Physical dimensions are 52.95 × 35.10 × 4.50mm — measure your existing cell before fitting if unsure.

• SL4 / SL5 / SL6 platform fit: These three handsets share the same battery bay geometry, connector pinout, and BMS handshake protocol — one cell covers all three models without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on SL-series hardware. The BMS accepted the cell cleanly, registered full charge state, and held resting voltage above 3.6V between sessions.
• First-charge protocol for Li-ion DECT handsets: After fitting, seat the handset in the base and leave it for a full uninterrupted charge before first use. SL-series bases use a trickle-top phase that Li-ion cells need to complete before the BMS reports accurate capacity to the handset firmware.

Talk time shorter than expected after fitting a new cell

A new Li-ion cell ships at partial state of charge — typically 40–60%. The handset firmware reads this low starting point and recalibrates its capacity estimate downward. Run two or three full charge-to-discharge cycles and the firmware re-learns the actual 950mAh ceiling. After that, talk time should match or exceed the original battery's output at the same charge level.

Base station charge light not activating after battery swap

SL-series bases check for a minimum voltage on the battery contacts before starting the charge circuit — if the cell voltage sits too low from storage, the base reads it as a fault and withholds current. Hold the handset firmly in the base for 60 seconds: some base firmware versions require a sustained contact signal before the charge IC enables. If the light still does not activate, check that the handset battery contacts are clean and the cell is correctly seated — the charge pin is the middle contact on the SL battery strip.