Your fundamental premise that sulfuric acid evaporates from a battery is flawed. The water evaporates. The sulfuric acid either remains as an increasingly concentrated solution, or it more likely forms sulfates.
Here is a chart showing the vapor pressure of sulfuric acid in aqueous mixtures:
https://www.electro-tech-online.com/custompdfs/2013/02/Sulfuric_Acid_Partial_Vapor_Pressure_20.pdf
Even at 60 °C, the vapor pressure of concentrated sulfuric acid is <0.0001 mm Hg. That is the reason that sulfuric acid can be used in desiccators as a powerful dehydrating agent without contaminating the materials being dried.
If you ever see a dry lead-acid battery, it is either sulfated, the sulfuric leaked out, or it was never filled.
As for why back-up batteries are not rejuvenated, I suspect you are confusing their routine and/or scheduled replacement with replacing the batteries because they are bad. Since they are a critical element in many systems, it is simply prudent to replace them before they go bad.
There is a small market for such batteries, and of course, they can also be recycled. One of the people I fly model airplanes with has access to batteries that have been removed from back-up supplies in the course of normal preventative maintenance. They are still quite usable for non-critical applications. We use them to start our model engines. There are lots of other uses for them.
Oh by the way, tcmtech, I have both a refractometer and polarimeter on my mantel.
John