Casio CZ/ VZ/ FZ - Pro Series

People,

  recently I noticed that some patches on my VZ-8m became corrupted.
Interestingly enough, this applies to INT patches only -- is this
an indication that the battery's dead? The card patches all seem fine.

What kind of battery do I need to buy and is it hard to replace
it?

What's the procedure to do a factory reset, may that would restore
patches?

The patch names in the affected patches all contain kanji and other
cool and unusual characters, I like it very much but I would
also like to play the synth  :)


Maxim