the internal battery of my MR-1 has the following specifications:
3.7V, 2000mAh, ~44g
and the frame for the battery is 53 x 38 x 10 mm.
The NP-120 / D-L17 / DB-43 batteries (used e.g. for FujiFilm FinePix F11 camera) have very similar specs:
3.6-3.7V, 1600-2200mAh, ~43-48g
and
53 x 35,3 x 11 mm
Whether the battery really works in the MR-1 I don't know, however. I have not tried it, because the battery of my MR-1 is still OK.