Read this interesting and (long) article...
http://www.accutronics.co.uk/pages/l...sportation.php
but the section at the bottom entitled "Lithium ion Batteries as ‘Carry-on’ or ‘Checked-in’ Luggage on Aircraft" is most relevant.
My advice is to insulate the battery terminals with insulating tape and carry them in your hand luggage. In theory the batteries could be put in the car and checked in... and they would then be classed as "in equipment' but the regs were really designed with laptops in mind (not RC cars).
If they kick up a fuss at the airport ask them to find their IATA manual and ask them to read the section on excepted Lithium ion batteries under UN3480....
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