Get in touch with your preferred airline and explain to them what you are thinking of doing. That laptops etc are allowed on aircraft ( in hold luggage currently) and many of these use Lithium Ion batteries. Use terms that will help you explain what you are planning to carry, i'e, like a lap top battery, as the airline staff can readily comprehend this.
I am not suggesting that airline staff are daft, but model boats to many will either be sailing ships (why would those need batteries?) or speedboats (don't they have petrol engines?)
Have a good time away:O)