Battery degradation isn't that big an issue since EV battery packs aren't like your phone battery and have active battery management systems to keep batteries at the optimal temperature and current. (Except the Nissan Leaf. Those EV's have issues with battery longevity.) Just about all major EV manufacturers offer 8 year, 100,000 mile battery warranties for a reason.

Most cop cars are just sitting still for basically the whole day and they're not in use 24/7/365. Incorporating slow charging into them sitting at a corner for half a day would be a breeze. This city is already building out curbside chargers. My neck of the woods got 3 stations with 6 charging cables and the cops in the neighborhood can just change where they idle their car by a block or two if they need a charge.