Yes you can use the V2 battery with V1 interface, but you won't be able to diagnose if you have a problem. The V2 battery doesn't have the led light like V1 battery.
Another thing to know is that you won't have the feature where you can trim the front derailleur for both the big and small chainring when setting up the shifting.
Last thing, you also need to buy the new V2 charger since the new battery has a different plug.
You can diagnose with the V2....the LED on the Interface will pulse X times to show you the problem, not in color like in the power unit.
At least this is what it was shown on the official Campy video.
Also, there's a specific V2 for Athena.
I do have to check on that charger thing as we were under the impression that the regular one would work...at least we were told that.
I was told by the distributor that you can use the V1 interface with the V2 battery, but you won't be able to diagnose if you have a problem. V1 interface doesn't have the diagnostics tool. no way around it.
Yes Athena has a specific battery and interface, but it was like that before too so not really news.
I saw the v2 and v1 charger side by side and the plugs are different. They are already available here in Canada.