Actually you are the bad one at math:
“He reported reaching the top of the grade with 80 percent, then recovering battery charge to 88 percent on the way down”
That keeps happening, always in surplus.
I am lousy at math!
But wouldn’t the truck start off at 100% capacity at the bottom.
80% left at the top.
Gain 8% on the way down.
So second trip start off at 88%, use 20% and reach the top at 70.4%. Gain 10%, so start third trip at 78%?
Although the rest of the article does make it sound like they have a surplus of energy - so I must be missing something.
But it started with 100% charge in the first trip and back to the bottom with only 88%. That doesn’t look like a surplus to me. On each trip it will have less and less charge and eventually have to be recharged.