on a good float charger batteries can last years. I have some powersonic batteries on a Redipulse, that have been on there for like 3 years. I pulled them off for a couple weeks to see how well they held up and they sat over 13v...
I like the fact that your boy probably has a better chance to build that truck himself than most members on here.lol He saw daddy build some awesome shit so he is past the "do I really want to try that" phase most of us went through the first time we went all out...