Hi!
I had the same problem, googling I did find the following:
http://kenichiuji.exblog.jp/i21/2/
it is in perfect Japanish but if you scroll down you will find the solution
Old tom is explaining, there you see the right batteries.
I did it twice with two SANYO and both are working perfectly, very simple to put two batts one on top of the other and close the watch.
Good luck!