How different are Battery Check tilesets from normal Jazz 2 tilesets?
 

Or are there no differences at all?

As I recall, the only difference is that JJ2 tilesets have that big copyright header at the start, and Battery Check tilesets do not.

(Before you rush off converting tilesets, I should point out that .j2t files contain little bytes which specify their filesize, and if that filesize marker is inaccurate, the tileset won't load.)