Be aware that one-way rentals in Norway are often subject to very high surcharges. Check prestige class from Hertz because you will need a provider which has a station in Bergen and Oslo. Maybe look at Avis also.
Mountain areas are eating battery capacity faster than plains, so in your head do not plan a theoretical value of km / miles which an e-car normally drives.
Charger network is listed here: https://elbil.no/lading/ladestasjoner/
Note: if a charger is not used actually it is called "ledig" - funnywise the German word if you are unmarried :-)
I hope you are also aware that there are different charging technologies used by different car manufacturers, so not every charging station fits to every car. Mainly there are AC and AC/DC chargers, some faster charging than others. They support also different plug types, e.g. Schuko, Type 1, Type 2, CCS, ChaDeMo (some Japanese cars) and Tesla (modified Type 2). At the end it is not so complicated like it sounds here, just want to make you aware.
In tourist hotpots be always prepared to brake because still a lot of people do not look before crossing the street, they rely on what they hear.
I had seen some German guys in June 2018 near a Tesla and two e-Smarts 50 km from North Cape, manually working at a cable because the ground was handled differently in Norway than in Germany. Tough and nice guys.
A really honestly written trip report for traveling Germany - Norway by a rented e-car (in German language) you can find here: https://www.funkloch.me/urlaub-elektroauto/?cn-reloaded=1
From the CO2 point of view the rental car is a much smaller issue than the flight to Norway.
It is doable and worth a try but I just wanted to point out some challenges that you might faced with.