The cars they tested were on loan from Tesla, but each Model S would cost the department $100,000 -- much, much more than the $30,000 it pays for one Ford Explorer. ​Further, authorities are worried that an all-EV fleet could prevent them from responding to situations in the middle of natural disasters, which could knock out charging stations.

Yegiyan remains optimistic about EVs' future with law enforcement, though. Tesla's Model 3 has an expected retail price of $35,000, after all, and other companies could follow suit with similarly priced electric cars. He told CNBC: