Stealth 400 Replacement Battery FT603048P 3.7V 900mAh

Stealth 400 / 500 Series — 3.7V Li-Polymer Replacement Battery (FT603048P)

This is a 3.7V, 900mAh lithium-polymer cell built to the FT603048P specification. It fits the Stealth 400 and 500 wireless headsets. Swap it in when the original cell no longer holds a charge or drops out during calls.

• 400 and 500 series compatibility: Both models run the same 3.7V power rail, share the FT603048P cell footprint, and use the same BMS handshake with the base station — that's why one cell covers both.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS held the cutoff voltage correctly at both ends and passed the charge-complete signal to the base station without fault.
• First-cycle base station protocol: Seat the headset in the base station and let it complete a full uninterrupted charge before taking a call. DECT headsets log the new cell during that first cycle — skipping it causes the talk-time indicator to report incorrectly until the handshake completes.

Base station not recognising the new pack after fitting

DECT base stations verify the battery pack through a BMS handshake before displaying a charge status. A cell shipped at storage voltage — typically around 3.6V — may not have enough charge for the base to initiate that exchange. Place the headset on the base immediately after fitting and leave it for a complete charge cycle without removing it. Once the handshake completes, the base will display charge status normally on every subsequent cycle.

Headset cuts out mid-call even with a charged battery

The Stealth 400 and 500 draw simultaneously from the audio circuit and the DECT radio during a live call. That combined load creates brief current spikes that can trip the BMS undervoltage cutoff if the cell voltage sags below threshold — even when the displayed charge level looks fine. This is most common in the first few cycles before the cell has settled. Run three to five full charge-and-use cycles and the sag behaviour typically stabilises as the cell reaches its rated 900mAh output.