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With 0 friction and 100% effeciency, the break even would be 45 tons of load? So this has 20 extra tons to make up for the various losses..

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Not 20 extra tons. 65 Extra tons.

Huh?

The weight is 45 tons going up, and 45 + 65 = 110 going down, right?

In a 100% efficient no friction wonder world, the load needed would be 45 tons going up, and 45 + 45 = 90 tons going down. This would balance out to 0 battery usage.

Since our going down weight is 110 tons and not 90 tons, we have 110 - 90 = 20 "extra tons" that can go to things like friction and imperfect conversion of energy forms.

With no friction etc you would just store all the energy on the way down and use it exactly the same (reversed) on the way up. 45 tons down is all you need to get 45 tons up. No extra. 90 tons down would get you 90 tons up.

I think you just described 0 friction with 50% efficiency. With 100% efficiency the weight of the truck alone would be enough to recoup the energy on the way down.

Opps you are right. So we need like 40% effeciency to make this work?

Yep.

efficiency * 110 tons * gh = 45 tons * gh

efficiency = 45 tons / 100 tons = 40.9%

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