I just had the pleasure of trying my Karma on your autobahns last thursday. Fully understand petrol is an issue. At full speed you have to refill every 1.5 hours.
Car is really not made for this. Luckily my daily commute is within electric range, but the petrol tank is too small for high speed driving.
By law, you don't have to drive at full speed, but you have the freedom to do so
You are right. We live 450 km distance from my wife's family... We simply should not use the Karma because of its inaccurate fuel tank gauge ... but we do!!! It's real fun!
I'm experiencing an other problem on long distance drives... Independent of the speed:
At about 50% battery, I go for sport mode, to keep battery up.
The battery still drains, but it will always keep up to about 50%...
If I have to refill the gas tank at a battery range of 35%, then, after continuation of the journey, it will only recharge to a range of 35%, becsuse this was The Range at The Sport Mode activatopn.
This repeats, until the battery changes in between 0-5 km...