Deep cycling House usage (as opposed to Starters cranking the engine)
requires specially designed battery types if you want them to last.
You also want to keep your Starter at Full all the time so you don't risk getting stranded.
The two circuits can be connected while charge sources are active, but otherwise isolated from each other.
ACR/VSR/combiners, IGN solenoids and DCDC chargers are the three main device types used to do that automatically, differences in cost an functionality depending on your use case and system design.
Do not rely on a manual switch requiring human memory.