If you want to learn more about batching and draw calls in Unity, you can read more about it here : https://docs.unity3d.com/Manual/DrawCallBatching.html
It has limitations that you may have crossed. For example, Unity's dynamic batching has a vertex data limit. Beyond that, it will not be able to batch the draw calls.
If you are using Unity 2017.1, the Frame Debugger will help you find out why exactly each separate draw call was created instead of batched.
For example:
But under normal circumstances, skeletons using the same Material will batch just fine, even if they are different resulting meshes.