The board has a "zero power RAM" unit - actually not "zero power", it has the battery built into the RAM chip. I don't know if the warning you are getting reflects a dead battery.

Once the board powers up for the first time, the battery kicks in, and will eventually die. I have a few Capcom games, so have wondered when one will go....

I bought a few of the specific 6116/6264 version of the anyPin NVRAM Battery Eliminator which Rob says works great in Capcom games. I have not yet had one die, so haven't tested one myself. http://lockwhenlit.com/anyPin.htm

I would not attempt the replacement myself, the chip is soldered in and should be left to a pro to fit.