A few years ago I brought a personal power pack and jump starter.
I removed the battery completly from a 1.6L car and connected this unit and started the car with no hesitation.
It is around the size of 3 to 4 smart phones and includes several lights switches and buttons. It weighs 600 grams and charges fast and holds charge for more than 6 months.
So a few years later I guess we would have better batteries again - I also see a charging system of both solar covered surfaces of the entire craft and descending via auto type rotation to feed power back to the batteries.