Back in times of old, when flags were allowed to be flown, snowflakes were white stuff falling from the sky and Gen Z were nowt but a twinkle in Gen X eyes, we used to have turkey baster type testers, battery top up fluid etc.
It was part of the cars general maintenance to top up the battery electrolyte.
Now they are all supposedly sealed maintenance free (although it's usually just a sticker over the same top up bungs.
Would a modern battery not also benefit from the old style test and topup routine?