I have used a small (~12AH) battery, connected to the main battery
with a Scottky diode(80 amp), or a break relay.
The break relay was connected to the radio power, which is
switched off while starting, and so can feed the relay coil.
THis would be my suggestion. Solve all the problems really.

Your starting switch might have such a contact.
That way, starting the engine, or using an electric winch, does
not mess up your power.

I would suggest the op go with this option. IN fact, I
strongly suggest it.

Regards,




Richard Webb, amateur radio station nf5b
Active net control on the Maritime MObile SErvice net, 14.300 mhz
See www.14300.net for info about radio services for mainers.
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a good captain is hoisting his first drink in a bar
when the storm hits