I've had the "normal" S30R Baton II on my bedside table since it came out this summer. Looks exactly like this light with an emitter swap. The battery is most definitely proprietary. Modifying another battery to work with this charging setup would be tricky, and probably dangerous. Here's a comparison photo - S30R battery on the left, normal Olight 18650 on the right.
Yes the light will work with any cell you put in it, but it'll only charge the special cell. Its still a great light though, even though I'm not wild about proprietary batteries either. The combination of "full-power" 18650 size, great UI, magnetic tailcap and handy charging base is hard to pass up. Its also an easy light to mod if that's your thing. Mine's had a nice warm white XM-L2 5C emitter in it for months now.