Simrad HS35 Replacement Battery 3.7V 1100mAh Li-Polymer

Simrad HS35 — 3.7V Li-Polymer Replacement Battery (AEC603048)

This 3.7V 1100mAh Li-Polymer battery is a direct replacement for the Simrad HS35 handheld VHF marine radio. It fits the HS35 portable transceiver used for ship-to-ship and ship-to-shore communication on the water. Voltage and capacity match the OEM AEC603048 specification exactly.

• HS35 platform fit: The HS35 uses a slim Li-Polymer cell at 3.7V nominal — the battery bay, connector orientation, and BMS handshake protocol are specific to this form factor. Swapping to a different voltage or cell format triggers a dock rejection or radio startup fault on this platform.
• Bench tested on actual hardware: We ran this pack through charge and transmit cycles on the HS35 dock. The BMS accepted the charger handshake without fault LED, and the radio's bar indicator climbed correctly as cell voltage rose through the 3.6V–4.1V window.
• Salt air contact care: Marine environments accelerate corrosion on the battery contact strip. Before insertion, wipe the gold contacts with a dry cloth — salt residue causes resistance spikes that the BMS reads as a fault, preventing the dock from initiating the charge cycle.

Why the HS35 drops to reduced TX power during extended radio calls

The HS35 transmits at up to 5W RF output, which pulls significant current from a 1100mAh cell. When cell voltage sags below the radio's lower threshold under sustained transmit load, the firmware steps down TX power automatically to protect the BMS. This is normal behaviour — not a faulty battery. A fully charged cell at 4.1V handles the initial transmit burst, but an aged or partially charged pack sags faster and triggers the step-down sooner.

Bar indicator showing one fewer bar than expected after fitting a new AEC603048

New Li-Polymer cells ship at storage voltage — typically around 3.7V–3.8V, not 4.1V. The HS35 bar indicator reads voltage thresholds directly, so a new pack straight out of packaging will show one bar fewer than a fully charged pack. This is not a capacity defect. Place the battery in the dock and allow a full charge cycle to complete before judging the indicator — once the cell reaches 4.1V, the bar display will read as expected.