Haha once I had to take a large battery.
I expected this and took print out of FAA limits and how to calculate the wh of battery.
After 10 mins of explaining basic physics equations he allowed.
But this also means you can take illegal items.
FAA limit is 100 Wh I believe.
For 3.3v it’s 27000 mah.
But if it’s 10 V this drops to 10000mah.
But the security guys just check the mah written outside is less than 27k.