Do you have a voltmeter?  The voltage stamped on the + side of mine is 3v.  Mine tested at 3.35, which is just fine.  I would likely be replacing it at close to 3v, and definitely anything under that value.  I'm sure an Eventide tech would know the tolerance.

You don't have to remove it to check it with a vom.  Put the + vom probe wire on the top of the battery and the – on any metal frame part (NOT the circuit board!!!)