Modern batteries are way way better than they used to be, even alkaline is better and were quite expensive in the 90's.
But it's not only how much better they are, it's the prices, alkaline is standard today, and you barely even look at the price, because they are dirt cheap.
But you are right that in electronics there have been much improvements, a modern flashlight is easily a 100 times better because of both LED and better batteries. LED improved it probably by a factor of about 10.
But for many things like a laptop, the power consumption hasn't gone down that much, because the better batteries have actually made it possible to make more powerful laptops instead. the power consumption of a modest laptop CPU alone id 65 Watt, which would be HUGE in the 80's.
I agree the 99% sounds like much, but I can attest to at least 80% probably more like 90% better batteries than the early 90's.
Lithium batteries really was a game-changer, especially if you consider only rechargeable batteries.