batteries are not of much use right now. You can fuel the vehicles with them. (They have more power since the latest update, so they last a little longer)
It would be nice if the vehicles switch from a combustion engine sound to an electric sound, when fueled with batteries. This would be very satisfying to hear. The combustion engine sound is a little annoying after hours and hours riding these vehicles.
BTW: I like the sound of the train very much!!! Well done.