You didn't say you were inside a shop.
And Yes, be sure you leave the cable sticking out where you will see it during your departure walk around.
You are right in that once you get on the road, the main engine will keep its battery and should do the same for the house bank. But, you still should seek out your phantom drain or it will come back to bite you.
A lifelong waterman and his bride going dry places for as long as the fuel money lasts.