About this replacement
Icom IC-GM1600 Series — 9V Lithium Replacement Battery (BP-234)
This is a 9V, 3300mAh (29.7Wh) lithium replacement battery for the Icom IC-GM1600, IC-GM1600E, and IC-GM1600K maritime VHF radios. The BP-234 is the correct cell format and connector for this GMDSS-capable handheld. Voltage and physical dimensions match the OEM pack exactly: 122.20 × 58.10 × 19.50mm.
- IC-GM1600 series fit: The IC-GM1600, IC-GM1600E, and IC-GM1600K share the same battery bay geometry, contact rail, and BMS handshake voltage window — all three accept this BP-234 format without modification.
- Bench tested on actual hardware: We ran this pack through full charge cycles on the IC-GM1600 platform. The BMS accepted the handshake on first dock insertion, held charge acceptance across repeated PTT-heavy transmit loads, and showed no overcurrent trip during sustained RF output.
- First insertion contact cycle: If the charger dock shows a fault LED on first insertion, remove the battery, wipe the gold contact strip with a dry cloth, and reseat firmly. The IC-GM1600 charger requires a clean contact surface to complete the BMS handshake before charging begins.
Why the IC-GM1600 drops to reduced TX power during extended transmissions
Maritime VHF radios transmit at 5W on the high-power setting, which draws a significant current pulse each time PTT is pressed. On a degraded or deeply discharged battery, the internal resistance rises enough to cause a voltage sag under that load. The IC-GM1600's power management circuit detects the sag and steps down TX output to protect the RF stage. A fresh BP-234 at full charge keeps the pack above the 7.5V sag threshold that triggers this cutback.
Bar indicator showing one fewer bar than expected on a new BP-234
New lithium cells ship at storage voltage — typically around 7.8–8.0V — not at a full-charge voltage of approximately 8.4V. The IC-GM1600 uses a voltage-threshold bar indicator, so a pack that hasn't completed its first full charge will display one fewer bar than expected. This is not a faulty cell. Run one complete charge cycle in the Icom dock until the LED goes solid green, then reinsert the battery — the indicator will read correctly at that point.