Hi Dockhead, we have similar set up, except main engine
start batteries are 24v.
I agree with the others, best to have a radio battery
as a buffer
However, instead of a separate radio battery
, my 12v Gen start battery is installed in the pilothouse and fed from house bank via Victron 24/12v convertor or Genís alternator
Being outside engine
room, this single
battery is kept cooler and higher same as a radio battery should, but serves dual purpose.
The DC260-12 AGM
battery is same as my 24v house bank, so cranks over Gen very easily.
This sketch shows set up and radio/start battery is in locker floor just ahead of inside steering
and 24-12v DC Panel.
I am told on Nets that my SSB
comes thru crystal clear.