Hmmm, battery probably won't be an issue. Especially if the computer still does it after being turned off and back on. It's possible that the motherboard (or the analog board) developed an issue right after installing the MODE32 extension.

Are you just running four 16MB SIMMs on the board? The SE/30 doesn't like that. Try adding four of the 1MB SIMMs back to the board.

http://www.biwa.ne.jp/~shamada/fullmac/repairEng.html#JailBar

There's a table in the link above.

-J