Battery terminal corrosion prevention

Whadayaknow-

The battery was bad.

Put it back in and it did the same thing- initially dome light and ODO came on but no start and then several lights flickered, even after key was removed.

Put the AGM back in and it started and drove normally...
Except the door locks don't work.
Not from the button, and they don't auto lock at 30 MPH.
They DO work from the fob.
GREAT!

Battery is a 72 month 4 year guaranteed replacement and is just starting year 3.
Rural King by Exide.
It wasn't cheap.
I've previously sworn by them.

Funny it tested good both with my volt meter and my newfangled charger/maintainer.
I hope I don't get the runaround because it tests good on their tester.