Do I become an energy supplier if I resell electricity?

Whether this subjects you to the licensing requirement for energy supply depends on the legislation in your country: that threshold differs in terms of number of connections, volume, and whether you purchase yourself or only meter through. In many countries, a landlord who bills consumption to their own guests falls outside that requirement, but this changes as soon as you also sell to third parties, such as at a public charging point. Therefore, clarify this with the energy regulator of your country or with an energy lawyer before you put a system into operation.