I have flow with 6s 5000mah packs (two of them) many times. You will need to check with your airline / airport but the limit is actually quite high. And that’s per person so if you are traveling with multiple people (who don’t have their lipos own of course ) you could carry even more by sharing them.
I don’t quite understand how a 6s lipo brick is “safe”, but my old 90% empty tube of toothpaste is dangerous.