Typically when I go with my riding group we'll ride anywhere from about 60 km's to 120km's depending on how much time we have. If my wife were with me, I obviously don't have to rush back to see her so probably would like to do rides on the longer end of the spectrum. When she goes with me we like to ride to a destination, have lunch, ride some more, head home. So, I can see some days wanting that 100 km range. I'm not that many years from retirement so I can see when the weather is good we can spend an entire day riding and eating.
But I suppose as we spend more time on the bike she'll get in better shape, so who knows how much battery capacity she'll need. But I'd rather just buy the 800 wh from the start and not worry about it.
