Nate wroteTry PolygonSpriteBatch for both skeletons and particles. That is the only way to do it in a single batch.
That's how I did it from the beginning. Now, at a later stage in the project I'm trying to optimize the code, and I thought mixing the rendering with PolygonSpriteBatch and SpriteBatch would increase the performance.
I did a quick test and didn't notice any performance difference between PolygonSpriteBatch and SpriteBatch on my 2 year old Android tablet. I rendered the whole scene (mesh animations excluded) with both of them, and the performance was identical.
Another interesting finding was that the begin() and end() methods didn't have almost any performance impact either when I repeated them for each entity separately. So, I literally had hundreds of begins and ends run each render step, and I saw only a very small frame rate hit; maybe 2 - 3 frames.
Oh well, I have to find some other way to optimize my code.