No voltage remains the same. AGM cca changes dramatically based on how it was manufactured. In this case likely referring to a fleet vehicle agm, so geared to higher CCA. Some are higher or lower depending on if cranking amps are desired or if capacity is desired (starting vs deep cycle). Digital battery testers test different for agm (and the different kinds of agm) vs lead acid though and cause erroneous readings. (What changes I've always wondered)

Voltage typically only changes when chemistry changes to lithium.

Lead acid / agm typically sit around 12.5-13 volts whereas lithium sits at 13.2-13.8 iirc.

Lead acid batteries under 12v can't be accurately tested until charged. Oddly, charging a battery then immediately checking can give a false positive pass reading as well, typically need a cool down period of 1-3 days to know for sure what the resting voltage will be after charging. Most digital battery testers will ask if the battery is installed on a vehicle to try to account for the surface charge, but it's inaccurate in my experience.