HJC CB-50 Tandem Pro Compatible Battery 2.4V 700mAh Ni-MH

HJC CB-50 Tandem Pro Kit Standard Intercom System — 2.4V Ni-MH Replacement Battery

This is a 2.4V, 700mAh Ni-MH replacement battery for the HJC CB-50 Tandem Pro Kit standard intercom system. It fits the helmet-mounted communication unit that links rider and passenger over a short-range wireless channel. Swap it when the original cell can no longer hold a charge through a full ride.

• CB-50 Tandem Pro Kit compatibility: The CB-50 standard intercom unit runs a 2.4V Ni-MH cell at a fixed voltage rail to power both the audio driver and the short-range radio simultaneously. Any replacement must match this voltage exactly — a deviation causes the BMS to reject the pack or the headset to cut out under combined load.
• Bench tested on actual hardware: We cycled this battery through charge and discharge on the CB-50 unit. The BMS completed handshake without error, audio stayed consistent through the draw cycle, and the radio channel held without voltage sag triggering a shutdown.
• First-cycle protocol for Ni-MH intercom cells: Ni-MH cells shipped in storage state need a full charge in the CB-50 base before first use. The base unit calibrates its charge termination using delta-V detection — if the cell is too flat on first insertion, the base may read a false full charge and stop early. Let it run a complete cycle from flat before riding.

Why the CB-50 cuts out mid-transmission on a fresh battery

The CB-50 draws current from two sources at once — the audio amplifier and the short-range radio transmitter. When both fire simultaneously, the combined draw creates a voltage sag spike that the BMS can interpret as an under-voltage fault. A new Ni-MH cell that hasn't been conditioned has higher internal resistance, which makes this sag worse on the first few cycles. After two or three full charge-discharge cycles, internal resistance drops and the sag stays within the BMS tolerance window. If the cutouts persist beyond five cycles, check that the cell contacts inside the headset housing are clean and making full contact.

Base station shows full charge but headset dies after a short ride

This happens when a cell arrives at storage voltage — typically around 2.2V for a 2.4V Ni-MH pack — and the base unit's delta-V detection triggers a false full-charge termination. The base reads the initial voltage rise as a completed charge and stops before the cell is actually full. The fix is to manually discharge the headset fully by leaving it on without pairing, then place it back in the base for a complete uninterrupted charge cycle. After one proper full cycle, the base will terminate correctly and the headset will hold charge through a standard ride.