@Override
    public int attachChild(Spatial child) {
        if (!(child instanceof Geometry)) {
            throw new UnsupportedOperationException("BatchNode is BatchMode.Simple only support child "
                                    + "of type Geometry, use BatchMode.Complex to use a complex structure");
        }

        return super.attachChild(child);
    }
SimpleBatchNode  comes with some restrictions, but can yield better performances.
Geometries to be batched has to be attached directly to the BatchNode
You can't attach a Node to a SimpleBatchNode
SimpleBatchNode is recommended when you have a large number of geometries using the 
same material that does not require a complex scene graph structure.

@see BatchNode
@author Nehon
jme3-core/src/main/java/com/jme3/scene/SimpleBatchNode.java