I would put the batteries in the base of the model.  You can use many different methods to get power from the base to the model itself.  One is to use a DC power jack.

If you locate it in the center of balance, you can put the female part of the jack in a brass rod, so that the model is balanced on the jack.  

This way the model is removable from the base and you don't have batteries in the model. 

A good example can be found here:

http://www.scalemodeladdict.com/index.php/topic,198.0.html