I am waiting for my order for the Cube Kathmandu Hybrid Pro 625. While shopping, my local bike shop rep offered me other Cube bikes with a 500 battery (Touring and one if my memory serves me right) and offered to upgrade to a 625 battery for a few 100$. Not sure exactly how much, but much less than the cost of a 625 battery.The 625 battery is longer, by about 70mm. I have a 625 in my Allant 9.9 and a 500 in my Topstone Neo Carbon3 so I measure them. This is why it is not available in some smaller size ebikes. It just needs a long enough down tube to contain it.
I have not heard of any ebike in which the two are interchangeable. Once you have a bike with a 500watt battery, if you want the 625watt, you need a different bike. The only option you have is to purchase a second battery and an OEM cover for it so it can be quickly swapped out and then there is the issue of where to carry it on the bike. They are long and do not fit in most bike bags and you should never carry a Lithium Ion battery in a backpack.
So it is fair to assume that a 625 would fit in some 500 Cube bikes.
Just ask your dealer for a swap!
Now I just hope the the bikes will be delivered as promised.