Icom BP-275 Marine Radio Compatible Battery 7.4V 1500mAh

Icom IC-M91D / IC-M92D — 7.4V Li-ion Replacement Battery (BP-275)

The BP-275 is a 7.4V, 1500mAh Li-ion battery for the Icom IC-M91D and IC-M92D handheld VHF marine transceivers. It replaces the original Icom battery pack directly, using the same connector and contact strip as the factory unit. Voltage and capacity match OEM spec: 7.4V nominal, 1500mAh (11.1Wh).

• IC-M91D and IC-M92D platform fit: Both models share the same battery bay geometry, gold contact strip layout, and BMS handshake protocol — one pack covers both. The 7.4V rail is common across this Icom marine handheld series, which is why the BP-275 works across the pair without modification.
• Bench tested on actual hardware: We ran the BP-275 on an IC-M91D dock and monitored the BMS through initial charge acceptance. The pack cleared the dock's handshake check on first insertion with clean contacts, moved to trickle, then terminated at full charge without fault codes.
• Marine contact maintenance: Salt air accelerates corrosion on the gold contact strip. If the dock shows a fault LED on first insertion, remove the pack, wipe the contact strip with a dry cloth, and reseat firmly — the IC-M91D dock requires a clean contact cycle to complete the BMS handshake before it will begin charging.

Why the IC-M91D drops to reduced TX power mid-shift on a new BP-275

The IC-M91D transmits at up to 5W, and that RF output draws a short but sharp current spike each time PTT is pressed. A new cell shipped at storage voltage — typically around 3.7–3.8V per cell — has slightly elevated internal impedance compared to a fully charged and cycled pack. Under sustained PTT use before the first full charge completes, the radio's BMS may interpret the voltage sag as a low-battery condition and reduce TX power to protect the pack. Charge the BP-275 fully in the dock before first use at sea — once the cells are at 4.1–4.2V per cell, the sag under transmit load drops and TX power stabilises at the full rated output.

Bar indicator showing one fewer bar than expected after fitting the BP-275

The IC-M91D reads battery level from voltage thresholds, not a smart fuel gauge chip. A new pack arriving at storage voltage will sit at the lower end of the threshold range, which the radio displays as one bar fewer than full. This is not a fault with the replacement pack — it reflects the actual resting voltage of the new cells before their first full charge cycle. Place the pack in the dock and charge to completion; once cell voltage reaches approximately 4.1V per cell, the indicator will show the correct full-charge bar count.