Batteries self-discharge after they are charged. Last year I put gas in my tank in early March, and didn’t drive anywhere for several weeks. The tank was as full as before. The batteries in my camera lose their charge slowly over a period of several weeks. If you charge your car batteries and then don’t use your car, they will have lost part of their charge. Electrical engineers please supply the details.
In addition, batteries lose their ability to hold a charge, and can only be charged to a percent of the capacity they had when they were new. An old smartphone of mine wouldn’t hold its charge any more, no matter how long I left it charging. Replaced the battery and will watch the cycle play out again. With an electric car your batteries will become dead weight, and you’ll have to replace them for big bucks.
The cost of replacement, the lost power, the cost of building charging stations, and the subsidies must all be factored into the equation.
Computers in cars and appliances stay set by using a trickle of electricity even when shut off. If you park your car at an airport for a three week vacation, the car battery will likely be dead when you return due to that small but prolonged discharge. If you disconnected one of the battery cables before you left, the battery would be ok when you got back but the car would have forgotten everything that had to be set or learned.