The paper says "We estimate that between 1992 and 2016, real price per energy capacity declined 13% per year". Where do you get your data for the last 5 years?

Regardless, 1 year isn't the correct duration for a bet. People average owning a car for ~6 years, and the average lifespan is something like 12 years.

But depending on terms, I might take a year-over-year bet for battery prices. Demand is high and the pandemic has caused significant supply chain problems. They could well have gone up this year. And indeed, a quick look at news reports suggests key components, including lithium and cobalt, are surging in price. Fine examples of why assuming a historical average has future meaning can get you into trouble.