RC enthusiasts use LiPo batteries, which can cause a lot of damage if mishandled and damaged, you can see a video here where a famous quadcopter pilot shows how many batteries he carries for a day of flying [0].

These batteries go into your carry-on luggage and needs to be protected from damage and short circuit.

Some info on why batteries shouldn't be in the cargo hold "Halon 1301, the suppression agent found in Class C cargo compartments, is ineffective in controlling a lithium metal cell fire." [1]

Here is the FAA requirements:

- LiPo batteries installed in a device are ok in either checked or carry-on luggage.

- An unlimited number of spare (uninstalled) LiPo batteries with a rating of up to 100 WHr may be carried, but only in carry-on baggage.

- With airline approval, up to 2 LiPo batteries with ratings between 100 and 160 WHr may be carried, but only in carry-on luggage.

- LiPo batteries larger than 160 WHr are not allowed.

It seems really strange you can travel with these things, I can't imagine the damage that will happen if a bag of batteries happens to blow up.

[0] https://www.youtube.com/watch?v=vCtneglrE8I&t=278

[1] http://www.faa.gov/other_visit/aviation_industry/airline_ope...