About this replacement
Icom IC-M37 / IC-M37E — 3.7V Li-ion Replacement Battery (BP-296)
This is a 3.7V, 2000mAh Li-ion replacement for the Icom BP-296 battery pack. It fits the IC-M37 and IC-M37E handheld VHF marine transceivers. The pack slots into the same battery compartment as the original and uses the same contact layout.
- IC-M37 and IC-M37E compatibility: Both the IC-M37 and IC-M37E share the same battery bay, contact strip, and BMS handshake protocol. The BP-296 form factor is identical across both variants, so no adapters or modifications are needed when swapping between units.
- Bench tested on actual hardware: We ran this pack through full charge cycles on the IC-M37 dock and monitored the BMS response across transmit and standby draws. The BMS handled the PTT current spike cleanly without triggering overcurrent cutoff at standard marine VHF TX output.
- First insertion into the charging dock: If the dock shows a fault LED on first insertion, pull the battery and wipe the gold contact strip with a dry cloth before reseating. The IC-M37 charger requires a clean contact cycle to complete the initial BMS handshake — this is not a faulty pack.
Why the IC-M37 cuts out mid-transmission on a new BP-296
A new Li-ion cell ships at storage voltage — typically around 3.6V — not at full charge. When the IC-M37 draws transmit current from a cell at storage voltage, the internal voltage can dip below the BMS cutoff threshold under load. The radio cuts out not because the pack is faulty, but because the BMS is protecting a cell that hasn't yet been fully charged. Run a full charge cycle before first use and the cutout behaviour stops.
Bar indicator showing one fewer bar than expected after fitting the BP-296
The IC-M37 reads battery level using voltage thresholds, not a fuel gauge chip. A new pack at storage voltage reads lower than a freshly charged cell, so the indicator can display one bar short even on a pack that has never been used. This is a voltage reading, not a capacity problem. Charge the pack fully to 4.2V and the bar display will reflect actual charge state.