About this replacement
Icom IC-M37 / IC-M37E — 3.7V Li-ion Replacement Battery (BP-296)
The BP-296 is a 3.7V, 2300mAh Li-ion battery for the Icom IC-M37 and IC-M37E handheld marine VHF transceivers. These are compact ship-to-ship and ship-to-shore radios used in demanding on-water environments. This battery slots directly into the standard battery compartment on both variants.
- IC-M37 and IC-M37E compatibility: Both models share the same 3.7V power rail, BP-296 footprint, and BMS handshake protocol. The battery connector pinout and contact spacing are identical across the M37 and M37E, so one part number covers both.
- Bench tested on actual hardware: We ran the BP-296 through full charge and transmit-load cycles on the IC-M37 platform. The BMS handled PTT-triggered current spikes without tripping, and the charger dock accepted the pack without a fault LED on first insertion.
- First-insertion contact check on the IC-M37 dock: If the dock shows a fault LED on initial seating, remove the battery, wipe the gold contact strip with a dry cloth, and reseat firmly. The IC-M37 dock requires a clean contact cycle to complete the BMS handshake before charging begins.
Why the IC-M37 cuts out mid-transmission on a fresh BP-296
A new Li-ion cell ships at storage voltage — typically around 3.6V — not at a full 4.2V charge. When the IC-M37 transmits, it draws a sustained current spike that can push a low-state-of-charge cell below the BMS undervoltage cutoff threshold. The radio shuts off mid-PTT not because the battery is faulty, but because the BMS is protecting the cell from dropping further. Charge the BP-296 fully in the dock before first use to bring the cell to 4.2V and give the BMS the headroom it needs.
Bar indicator showing one fewer bar than expected after fitting the BP-296
The IC-M37 uses a voltage-threshold bar indicator — each bar corresponds to a resting voltage band. A new cell at storage voltage reads lower than a fully charged pack, so the indicator may show one or two bars even on a brand-new battery. This is not a capacity fault. Charge the pack fully in the dock; once the cell rests above approximately 4.0V, the indicator will reflect the correct charge state.