Plantronics K100 Compatible Battery 3.7V 650mAh Li-Polymer

Plantronics K100 — 3.7V Li-Polymer Replacement Battery (PR-423350)

This 3.7V, 650mAh Li-Polymer battery replaces the original PR-423350 cell in the Plantronics K100 Bluetooth headset. It fits the lightweight over-the-ear K100, which pairs to mobile phones for calls and audio. Voltage, connector, and cell dimensions match the original unit exactly.

• K100 platform fit: The K100 runs a single-cell Li-Polymer pack at 3.7V nominal. The PR-423350 footprint — 52.30 × 33.53 × 3.90mm — is the only cell geometry that fits the K100's housing without mechanical stress on the flex connector. No adapter, no trimming.
• Bench tested on actual hardware: We cycled this cell through the K100's BMS on the bench. The protection circuit accepted the new pack without fault codes, and the charge termination voltage hit 4.19–4.20V across three consecutive charges — within the expected window for this chemistry.
• First-charge protocol for the K100: Place the K100 in its charging cradle and run one complete charge cycle before your first call. The K100's firmware uses that initial cycle to recalibrate its charge state register. Skip it and the battery indicator will read inaccurately for the first several uses.

Talk time shorter than rated on the first few cycles

A fresh Li-Polymer cell doesn't reach full usable capacity on cycle one. The electrolyte needs three to five full charge-discharge cycles to wet the electrode surfaces uniformly. Until that happens, the K100 will cut off earlier than the rated figure. Run full cycles — charge to termination, use until the low-battery alert triggers — and rated capacity stabilises by cycle four or five.

Base station shows full charge but headset cuts out after short use

A replacement cell shipped at storage voltage — typically around 3.6–3.7V — looks "full" to the base station before the BMS has completed a real charge cycle. The K100's charge state register hasn't been reset, so it reports 100% off a stale reading. The fix is straightforward: run one complete charge from the base cradle before use. After that cycle, the BMS holds accurate state-of-charge data and the cutout symptom clears.