I recall a while ago someone set up a distance-calculator website where you entered a Start point postcode, followed by two distances from this and it would draw you a map, showing how far you would get from this postcode at the stated mileages. (basically, it drew an inner and outer zone, with your selected postcode at the centre). Anyone used it? Or remember where it was?
You would use your home postcode as the start point - and set the inner core at 20 miles, and the outer 40 miles. The resulting map would then show you (firstly) the point of no return limit for a maximum distance assuming you did not recharge and wanted to get back home. The second limit would be your maximum range, and you’d be looking to recharge somewhere within this second circle.
Does it ring any bells?