Ran roof air all day on only solar, batteries still full

Now I really would like to hear the story about free batteries. ;)
Batteries went long way in just last years.
I still remember my first laptop, not much more than 10 years ago, where new battery would power for 1 hr and with 12 months warranty, it promptly died on month 14.
Now in 4 yo laptop with 17" screen the battery still powers long movies with power to spare, or 3 hr of forum chatting.