How to get batch working for multiple on screen characters with bone based animation (iOS)?

A game targeted iOS 4gen devices, have up to 9 on screen characters, each consist of 4k verts, 21 sub meshes and animated via bones. All sub meshes shared one material. The 9 characters are all the same (prefab).

Reported by Unity stats: for 1 instance have 21 draw calls, 2 instances have 42 draw calls and 0 batches. As far as I know it's safe to keep under 100 draw calls for my target platform. So how could I get batches working?

You wouldn't; batching doesn't work for animated meshes. You must have a bunch of materials for each character, because you would typically have 1 or 2 draw calls per character if you're using just one material, depending on the shader.