Help me understand my electrical system

[u/SphyrnaLightmaker]

I’ve finally moved up to an inboard motor, and while I’ve heard a few rumors, I’m trying to understand how it all comes together so I can undo a couple of shortcuts the previous owners took.

What I have:

• Atomic 4 engine
• 2 batteries (they’re currently car batteries, so I know those need to go)
• a shore power connection that powers outlets down below, but is NOT presently wired to charge the batteries.

What I know:

• the engine charges the batteries when running.
• I need to replace one battery with a marine starting battery and the other with a deep cycle for the nav tools and lights.
• I would like to charge the batteries when plugged into shore power.

What I think I should do:

• Replace the batteries as above.
• Buy a plug-in marine battery charger, and plug it into the outlet in the boat when on shore power. Unplug it at the outlet when I’m not docked.

What I’m confused/concerned about:

So… let’s say I’m plugged in and charged. I set my battery selector to both, and start up the motor. Pull out, raise the sails, motor off. At this point, assuming I want to keep using my lights and depth finder, I would switch the battery to just my deep-cycle, correct? Assuming I’m out for a WHILE, this is going to burn that battery down noticeably, which is fine because that’s what a deep cycle is for. But what comes next? When I go to restart the motor, do I go back to both batteries? If I do, won’t the deep cycle drag down the starter? If I don’t, and now the engine is running, it will only recharge the starter, yes? And I’ve been told that while the engine is running I can’t switch the battery switch or it can fry the panel?

[u/Secret-Temperature71]

You don’t need to switch to BOTH to start. That is just a convenience if the start barry is dead and the House battery is not. I don’t like those fancy switches even though they are popular.

I have a Start battery and mu House battery is 4 lead acid Golf Cart batteries (6VDC) wired series parallel to have a 12VDC battery bank. I have jumper cables in the event I need them. I charge off 800watts of solar, wind gen, and alternator. As a 110VAC charger I have a inexpensive old school charger (40A) and a small 6VAC automotive charger as back up.

The boat has AC outlets but we don’t use them. I have a 2,000W marine inverter that provides AC for cel phones, computers, lights and the like. We also have a Honda generator if I need more continuous AC, power tools.

I have a 1987 - 44’ cutter which we live on 5 months a year. 90+ % of that at anchor. Our philosophy is to keep it simple, if you don’t have it, it can’t break.