My 721 uses a pair of CR2032 cells, which are nominally 3V each, and the current pair measure at
3.005V and 3.020V
Note that the calipers keep drawing current when the display is off, so your battery life may not be as good as you would like (just a few months).
What I do is slide the battery housing toward the jaws just a little bit before putting them away. This disconnects the batterys from the little pin which carries power into the electronics. This means that I will have to re-zero the unit (the push of a button) when I slide the battery housing back into place -- but it also means that the batteries are not being drained while I'm not in the shop using them. This results in a major improvement in battery life.
I don't have that, but yours is the 722, not the 721, and I think that is designed to connect to a remote set of electronics for doing statistics on a production line -- measure every part off the line, and note trends in the dimensions which may indicate that a tool is wearing enough to need the insert replaced, or something like that. I don't have it, and I don't miss it, as I am not doing production work.
Overall, I am quite pleased with my calipers, other than that battery life feature. but it is so simple to disconnect the batterys during storage that it is no problem. The 12" Mitutoyo calipers that I have give longer battery life (over a year), and have a real "off" button. But since disconnecting the batteries involves unscrewing a cover to access the batteries, disconnecting them to get even more life would be a real PITA.