I don't know for sure but a good guess would be that the police are also looking at the ongoing costs. Most of energy used to move cops around now is probably used just for cruising, with the average time of high speed chases (probably) very low compared to cruising.
So with this in mind, maybe this is a great way for them to save money. Not only do they not have to buy gas anymore, but they also don't have all kinds of maintenance to do either :
I read on the site that charging takes only 1 hour, and the batteries are swappable too. So technically I guess that means that when a Bike gets low in the middle of the day, he just has to pull up to the police station and swap the dead battery for a fully charged one in a few seconds and off he goes again.