This is unverified. Please confirm or report back if any of these batteries work.
・PANASONIC-----VW-VBX090-W / VW-VBX090
above all are the battery equal to DB-110, except capacity.
This $7.99 battery MAY NOT WORK.
You will void your warranty if you take apart your camera. Your best option is to call RICOH support or go back to the store where you bought the camera from in the first place. The RICOH battery is not supposed to be changed by the end-user, only professional support centers.
If you attempt this, suggest you read this post first.
BTW, this article on the m15 shows that the DB-100 was used in the previous version of the camera.
Several people on this forum have taken the camera apart and put it back together again. No one that I know of has changed the battery.
If you get it working, please report back. I don't recommend this unless this is a hobby for you or you are unable to take the camera back to the store.