It depends on how fast you want to go. I have a fairly large 835Wh battery on my Cross Current. On the top assist level (600-700W of continuous assist power) I can go about 30 miles. Figure 30-35Wh per mile to cruise at 28mph. To cruise at 20mph you’d be using about half as much power so you would (theoretically) almost double your range. If you’re willing to ride on the lowest assist level you can massively increase your range. In general you should be very wary of manufacturer claims about range as there is no standard and there is a lot of exaggeration that goes on with marketing claims. I personally like to ride fast on my e-bike so the range numbers quoted for the lowest two assist levels are not relevant to my personal use case.