About this replacement
Icom IC-A3 / IC-A22 Series — 12V Ni-MH Replacement Battery (CM-166)
This is a 12V 1000mAh Ni-MH replacement battery pack for the Icom IC-A3, IC-A3E, IC-A22, and IC-A22E portable aviation transceivers. It replaces OEM part numbers CM-166, CM-166S, and BP-166. Capacity figure is taken directly from product data — 12Wh total energy.
- IC-A3 and IC-A22 platform fit: Both the A3 and A22 variants run the same 12V battery rail, share the same physical connector, and use the same BMS handshake protocol — one pack covers the full series without any modification.
- Bench tested on actual hardware: We cycled this pack through transmit loads on the IC-A22 platform. The BMS handled PTT current spikes without tripping, and the charger dock accepted the pack cleanly after a standard contact cycle.
- First insertion into the charger dock: If the dock shows a fault LED on first insertion, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The Icom dock requires a clean contact cycle to complete the BMS handshake before charging begins — this is not a defective pack.
IC-A3 bar indicator reading low on a brand-new CM-166 pack
Ni-MH cells ship at storage voltage, typically around 1.0–1.1V per cell, not at full charge. The IC-A3 uses a voltage-threshold bar indicator, so a pack at storage voltage will display fewer bars than expected — sometimes just one. This does not mean the pack is faulty. Run a full charge cycle through the dock first, then check the bar reading again at full voltage before drawing any conclusions.
Radio cuts out mid-transmission on the IC-A22 with a new pack fitted
Mid-transmission cutout on a new pack is almost always a BMS overcurrent trip triggered by the PTT transmit current spike. Ni-MH packs that haven't completed a conditioning cycle can have higher internal impedance, which causes a voltage sag under RF output load. The BMS interprets the sag as an overcurrent event and cuts the output. Complete one full charge-discharge cycle through the dock, confirm resting voltage sits at or above 13.2V after charge, then test PTT again.