Quoted from Patofnaud:Yeah that battery holder is SHOT. There are threads devoted to moving it off the module and Pinwiki covers it also so I'll leave that be.
That is why you are powering up with the "2500 3". However stepping through the up down advance dance should get you past that.
To answer your other questions:
Doing the power off/on cycle will not clear the condition if the batteries are out/shot. That only fixes the condition if the 'memory protect' button has been pushed or you just put in a set of batteries.
The state of the center button does nothing when you power up a machine, it is only sensed/matters when you hit the selftest/advance button.
Cool, so I'll remove and replace it. I'll take a look at pinwiki instead of cleaning anything. Glad you pointed that out! It didn't look so bad to me so I thought I could clean it. What about it really said to you that it was shot and needed to be replaced? For future reference, I mean. Or is any corrosion just enough to say 'done'?