Panasonic WX-C2020BAT Wireless Headset Replacement Battery 3.6V

Panasonic WX-CT2020 / Ultraplex II — 3.6V Ni-MH Replacement Battery (WX-C2020BAT)

This is a 3.6V, 1500mAh Ni-MH replacement battery for the Panasonic WX-CT2020 and Ultraplex II wireless headsets. It slots into the headset's battery compartment and powers the combined audio circuit, speaker, microphone, and DECT radio transceiver. OEM part numbers WX-C2020BAT, 2020BAT, and PA04940398 all cross-reference to this cell.

• WX-CT2020 and Ultraplex II compatibility: Both headsets run on the same 3.6V single-cell Ni-MH architecture and share an identical battery footprint, connector orientation, and BMS handshake protocol with the base station — which is why one part number covers both units.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the WX-CT2020 base station, confirming the BMS completed its handshake, the charge indicator activated correctly, and the protection circuit tripped at the expected low-voltage threshold without dropping the headset mid-cycle.
• First charge protocol for DECT headsets: On first use, seat the headset in the base station and run a full uninterrupted charge cycle before taking a call. The base needs to log the new cell before its talk-time estimate registers correctly — skipping this step causes the indicator to report inaccurate charge levels for the first several uses.

Base station not recognising the new pack after installation

The WX-CT2020 base station performs a BMS handshake when a battery is first seated. If the cell arrives at storage voltage — typically around 3.2V on a Ni-MH pack — the base may not register it as a valid battery and will withhold the charge signal. This is not a fault with the battery or the base. Place the headset in the cradle and leave it undisturbed for at least 30 minutes — the base station needs that window to detect the cell and initiate the charge cycle. Once the charge LED activates, the handshake is complete and normal operation resumes.

Headset cuts out mid-call even with a recently charged battery

Mid-call dropout on the WX-CT2020 is usually a voltage sag issue, not a dead battery. The headset draws current simultaneously from the audio amplifier, microphone circuit, and DECT radio — that combined load pulls the cell voltage down sharply during active transmission. If the Ni-MH cell is not fully conditioned, its internal resistance is higher than rated, and the protection circuit interprets that voltage dip as a low-battery cutoff event. Run three to five full charge-discharge cycles through the base station to condition the cell and reduce internal resistance — after conditioning, the resting voltage between calls should stabilise above 3.4V.