To reduce batches, I put together as many billboard images as I can onto a big master texture, 4096*4096 (which compressed down to just 8 meg once in DXT1 format.) Here's an example:

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The first problem is that some bills need their origin at the centre (such as explosions) while other bills need their origin at the base (such as fire).
The second problem is that often the exact centre (or exact middle bottom, or whatever) isn't the ideal place for a handle.
I'm using captures of real explosions, and for maximum quality I'm avoiding resizing where I can. At the same time, I need to squeeze the images as close together as possible. This often means that the best bounding box will result in an an off-centre origin of the explosion, because the cloud will drift a little left or right.
Programmers are probably thinking "Just shift/resize" but that is not ideal, it means degrading the quality of the source or wasting space on the texture.
