Do a search on here for battery
combiners, chargers, and such. There have been hundreds of threads on this, many very recent (as in last couple of weeks). There are pros and cons to the different ways to do it.
It goes beyond just charging
a start and house battery design. It really should be a "holistic" design that includes: which battery will be charged by the alternator
(house or start), type of switches, Echo-Charger/Duo Charger/other dc to dc chargers, types of batteries if they are different, etc.
The solution may be simple but the decisions are not trivial.
It's not clear to me how an inverter
is part of your question though for an outboard
boat on the water
. You can use an inverter/charger to charge batteries while on the dock
with shore power
but it won't do anything for you on the water
. Your outboard will have an alternator
that usually goes to a start battery. An echo charger
may be all you need or a 1-2-all switch. I'm not a big fan of 1-2-all switches for what you want to do. It is too easy to leave it on "all" while you are running the motor
and then both batteries will run down at the same time if your charging
fails. A duo charger
can do a better job of charging two different types of batteries.
But if you are very careful and isolate your batteries after charging them both up, a 1-2-all switch is the simplest way to go.
Look at the Blue Sea site. It has some configurations but remember they are trying to get you to buy their products not necessarily give you what is best for you. They do work though. Here is one product they sell: https://www.bluesea.com/products/764...tery_Kit_-_65A
Here is their wiring
But this system uses a battery combiner and there are pros and cons to that setup.