What is the real autonomy of an e-bike?

When you surf the net looking for electric bicycles information, bike manufacturers and shops offer it as X kilometers for a complete full battery. They say 50, 80, 100 or 120 kilometers that the e-bike can run with the battery. However, the lack of an international standard makes it impossible to compare e-bikes models. There is a clear, famous statement: the more Wh a battery has, the more kilometers can ride a biker.

Moreover, several factors come into play. For instance, take the same e-bike and the same cyclist, but different wind direction or speed, how many her saddlebags weight, aerodynamics of garment and accessories, wheels pressure, slope of a road, what gear she uses the most or whether she pedals in a cold or warm day (lithium batteries are more affected by low temperatures, thus they perform up to 20% less).

The traditional flux of questions-answers starts by the client, arrives to the shop owner, then the distributor and finally reaches the e-bicycle manufacturer. It would be so easy to make it simpler if there was an international standard. For example, every e-bike on a standardized bicycle roller with a dynamometer would allow to calculate the power and the exact battery consumption. Taking these numbers, manufacturers could apply a -+10 or a +-20 to give bicyclers real data about their products. In the meantime, bikers look for personal experiences about e-bikes in internet forums and specialized webs.