Cardo Q2 Replacement Battery 3.7V 400mAh Li-Polymer

Cardo Q2 / Scala Rider TeamSet Series — 3.7V Li-Polymer Replacement Battery (H452050)

This is a 3.7V, 400mAh lithium-polymer cell that replaces the original battery in the Cardo Q2, Q2 Pro, Scala Rider TeamSet, and Rider TeamSet Pro wireless motorcycle headsets. It matches the OEM part numbers H452050 and 09D29. At 49.00 × 20.10 × 4.70mm, it fits the original battery cavity without modification.

• Q2 and Scala Rider TeamSet platform: These models share a common battery footprint, connector pinout, and BMS handshake protocol — the same 3.7V cell services the full group, which is why a single part number covers the range.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Q2 unit, confirming the BMS accepted the pack, the protection circuit responded correctly to low-voltage cutoff, and the headset reached the rated 3.7V nominal rail under combined Bluetooth and audio draw.
• First-cycle base station requirement: On first use, dock the headset in the base station and let it complete a full charge cycle before making a call. The base needs to log the new cell before its talk-time estimate becomes accurate — pulling the headset early skips this handshake and the indicator will misread remaining capacity.

Voltage sag under combined Bluetooth and audio draw in the Q2

The Q2 runs its Bluetooth radio and audio amplifier simultaneously off a single 3.7V cell rated at just 400mAh. When both loads peak together — during a call on a noisy road where the audio gain climbs — instantaneous current draw spikes briefly above the cell's comfort zone. A degraded original cell cannot hold the voltage rail steady under that spike, which is why the headset cuts out mid-transmission rather than during silence. A fresh cell with full capacity handles the combined load without the rail dropping below the BMS cutoff threshold.

Base station showing a full charge but headset cuts off after short use

This happens when the replacement cell arrives at storage voltage — typically around 3.6–3.7V — and the base station interprets that as a near-full charge, stopping the charge cycle early. The cell never receives a proper top-up, so the headset runs off a shallow state of charge and cuts out quickly. The fix is to fully drain the headset in a call, then re-dock and allow a complete uninterrupted charge cycle until the base indicator confirms 100%. After that first full cycle, the base station fuel gauge reads the cell correctly.