Knackered battery

[Dockhead]

That's like blaming a car for crashing into pedestrians. The fault is with the operator.

There is nothing wrong with rotary switches (1-2-both) I have been using them for 45 years and never once had a flat battery due to misuse.

That's great for you, Vyv, but not everyone is as smart and diligent as you are. I am certainly not!

Those switches are a recipe for operator error and I wouldn't have one on my boat. And in general, I don't think it's good practice to parallel battery banks during charging, including using a diode split charger. Every bank deserves to have its own charge profile.

Gold standard is dual alternators and completely separated start and house banks. In the absence of that, the next best thing is to charge one bank from the other using a B2B charger.

And properly regulate the alternator to give a four stage charge appropriate to the bank it's directly connected to.