About this replacement
Panasonic Attune II HD3 / WX-ST300 Series — 3.7V Li-ion Replacement Battery (WX-SB100)
This is a 3.7V, 700mAh Li-ion replacement battery for the Panasonic Attune II HD3 wireless headset system. It fits the WX-SB100 battery slot and also crosses to the WX-CH455, WX-ST100, and WX-ST300 handsets. Dimensions are 40.00 × 31.10 × 5.90mm — physically identical to the factory cell.
- WX-SB100 platform compatibility: The Attune II HD3, WX-ST100, WX-ST300, and WX-CH455 all run the same WX-SB100 cell. They share a 3.7V nominal rail and use the same physical connector and BMS communication protocol. Swapping between these models requires no adapter.
- Bench tested on actual hardware: We cycled this cell through the Attune II base station and confirmed the BMS handshake completed correctly. The station moved from fault to charge status within 90 seconds of seating the new pack. Cutoff voltage held at the expected 3.0V threshold under combined DECT radio and audio load.
- First charge in the base station: Seat the new battery in the base station and leave it through one complete charge cycle before making a call. DECT headsets log the new cell during this cycle — without it, the talk-time indicator reads incorrectly and the headset may cut off earlier than expected.
Base station showing a charging error after fitting the new pack
The WX-CH455 and Attune II base stations check the battery's BMS before starting the charge cycle. If the cell arrived at storage voltage — typically around 3.6V — the station may flag an error rather than begin charging. This is a BMS handshake timing issue, not a faulty battery. Remove the pack, wait 10 seconds, and reseat it firmly. The station should clear the error and begin charging within two minutes.
Talk time shorter than rated on the first few cycles
Li-ion cells ship partially charged and do not reach full capacity on the first cycle. On the Attune II HD3, the base station's talk-time estimate also recalibrates over the first three to five full charge-discharge cycles. Expect capacity to increase noticeably by cycle three. If talk time is still noticeably short after five full cycles, check that the base station is not in power-save mode, which reduces charge voltage and leaves the cell at roughly 80% state of charge.