Nonsense. The battery voltage is determined by the chemical composition of the battery components.

Weight? Prove it. This is just another irresponsible version of "the sky is falling!" This is old fogyism at its best.
"The world is going to Hell in a handbasket!"
This has been spoken as long as there have been new generations coming along.

I've been buying batteries for 45 years. The weight of a top line 27F has stayed pretty constant over the years. As battery construction becomes more advanced, auto manufacturers have been specifying smaller batteries to save weight which will improve the fuel economy.

STILL, battery manufacturers have to manufacture product that meets the automakers' specifications.
Battery manufacturers have to produce a good product or word of mouth will kill them.
Auto shops don't want bad batteries that come back to the shop
There are other magazines than Consumers' Reports who periodically test batteries.
As much as you'd like to not believe it, there are Truth in Advertising laws.
There are greedy lawyer groups trolling for new Class Action Suits.

Way back in the day, say 1975, one could expect 5 years of life from a battery. Exceptional ones would last seven. That is still true today. Battery life is on a bell shaped curve. Some of the long life stories from here obviously represent cases on the outer limits of the bell shaped curve.