Really? I got a Raiden 2 board and cab as a lcd conversion/rebuild project, and today I dropped the 2 board in the running cab to give it a whirl. Ran great, but I was disappointed to find that even with a fresh battery it would not save the scores. I though for sure that it would since it has the battery and all.
Sounds like you have what I'm after. Once I finish up the 2 I am going to have to track down the DX. Love the series.
Not really sure what the battery is for on R2/DX.
For Zero Team (a very similar board) the battery is used to keep the sprite decryption keys alive, if it dies you end up with scrambled sprites and have to either
a) run an (official? leaked?) suicide repair kit (supported in MAME)
b) replace the program roms with a set where the encryption key is uploaded every time
c) replace the graphic roms with non-encrypted versions.
Raiden 2 however always uploads the encryption keys, so the battery seems pointless. Maybe there are earlier undumped revisions which don't and are prone to the same graphic suicide issues, but I've never seen one, nor seen reports of it happening.