An alternative (no pun intended) is to carry a battery with slightly higher nominal voltage than the car:
I'm getting a 5A boost at the beginning of a trip and then it goes down towards 2A in an hour.
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2016: 128.75L for 1875.00km => 6.87L/100km (34.3MPG US)
2017: 209.14L for 4244.00km => 4.93L/100km (47.7MPG US)