Korg Poly800/EX800 Users

I recently dug my old EX 800 out of storage, turned the power switch 
and... nothing. I figured it's the battery because 1) it has never 
been changed, and 2) the last time I tried out the synth (about 
years ago or so) it worked fine, so what could have happened to it 
in storage, right?

I was wondering why should a dead battery prevent the synth from 
powering up at all. So I checked the battery and it's not dead! It 
still has 3V to it. I don't know if measuring it with no load (since 
it doesn't even turn on) makes a difference. I also measured the 
power supply and it's fine.

Should I run out and get a new lithium battery? Should I test it 
with 2 AA in series? Does the fact I see not LEDs on at all but I 
measure 3V from the battery mean the whole thing is dead?