About this replacement
Nokia HS-21W — 3.7V Li-Polymer Replacement Battery (LP402025L150)
This is a 3.7V, 150mAh Li-Polymer cell for the Nokia HS-21W Bluetooth wireless headset. It replaces the OEM pack (LP402025L150) when the original loses capacity or fails to hold charge. The cell measures 26.50 × 20.00 × 4.10mm and fits the HS-21W housing without modification.
- HS-21W platform fit: The HS-21W runs a single-cell Li-Polymer pack at 3.7V nominal. The LP402025L150 format is specific to this headset's internal cavity and connector orientation — the voltage rail and physical footprint must match exactly for the BMS to accept the cell and enable charging through the base station.
- Bench tested on actual hardware: We cycled this cell through the HS-21W base station and confirmed the BMS completed its handshake, accepted charge current, and released into discharge without fault flags. Voltage at full charge measured 4.18V — within the expected Li-Polymer ceiling.
- Base station logging on first install: Place the HS-21W in the base station immediately after fitting the new cell and leave it for a complete charge cycle before making a call. The base needs to log the new cell before its talk-time estimate becomes accurate — skipping this step causes the base to display misleading charge status.
Why the HS-21W cuts out mid-call on a new battery
The HS-21W draws current from two loads simultaneously — the audio codec and the Bluetooth radio. Under combined draw, a cell at storage voltage can sag below the BMS cutoff threshold, triggering a shutdown that looks like a call drop. This is not a fault with the replacement cell. A full conditioning cycle through the base station raises the resting voltage high enough that the combined load no longer pulls it below cutoff. If dropouts continue after three full cycles, check the base station contacts for oxidation.
Base station shows full charge but headset cuts off after a few minutes
A new Li-Polymer cell ships at storage voltage — typically around 3.7V — not at full charge. If the base station's charge indicator trips on that resting voltage before completing a real charge cycle, it can report "full" prematurely. The headset then cuts off quickly because the cell was never topped up to 4.2V. Place the headset in the base, leave it undisturbed for at least two hours, then check that the indicator cycles through charging before settling on full.