Which is what the parents meant. We dont need thicker laptop for bigger battery because we already hit that limit. And with lots of battery improvement coming in the next 5 years they could have made the same 100Whr battery smaller without sacrificing other features.
passengers may also carry up to two spare larger lithium ion batteries (101-160 Wh) https://www.faa.gov/hazmat/packsafe/more_info/?hazmat=7
100Wh internal battery like the 16” MBPB + 2x160Wh, I don’t see an issue with FAA rules.