It is a classic chicken-or-egg situation. People will be reluctant to buy an EV (Electric Vehicle) if they worry that it will run out of juice. But unless more EVs are sold, the charging infrastructure will not be built to serve them. Batteries to the rescue. Not the batteries inside the car, but outside at the charging stations.
The following excerpt/summary is how McKinsey puts it in their February article: How battery storage can help charge the electric-vehicle market.
There are two major problems.
First, there is convenience. Most public charging stations today are “Level 2,” meaning that they deliver 7 to 19 kilowatt-hours (kWhs) of energy every hour (think of kWhs as equivalent to gallons of gas).5 A BEV sedan with a 60-kWh battery would take five to ten hours to “fill up” at a conventional (as opposed to fast-charging) Level 2 station. Having so few stations and such long service times turns off would-be buyers
Second, there are the economics. Although direct-current fast-charging (DCFC) stations with 150 kilowatts of power can fill up a BEV (Battery Electric Vehicle, as opposed to a hybrid) sedan in about 30 minutes, they can cost up to $150,000 to install; a 50-kilowatt DCFC station can cost $50,000. The kilowatt number refers to the maximum amount of energy that can be drawn every hour; a higher kilowatt delivers more electricity faster. DCFC stations are also expensive to run.
One of the things that makes them expensive is something called the demand charge. All electricity customers pay for the energy they consume, as measured in kWh; this charge is like paying for gallons of water used. Nonresidential customers, including charging stations, also pay a demand charge for the maximum amount of energy used in any 15- to-30-minute period in a month.
So for a commercial charging station, as soon as a car plugs in, the station owner must pay a demand charge…and the more vehicles that plug in at the same time, the higher that 15-30 minute period demand charge.
Batteries can solve both problems
That’s where batteries come in. On-site batteries can charge and discharge using direct current (DC) and connect to the grid through a large inverter. They can then charge from the grid at times when costs are lower, store the power, and release it when demand is higher (a practice known as peak shaving). When a car arrives, the battery can deliver electricity at 150 kilowatts without drawing power from the grid. If two vehicles arrive, one can get power from the battery and the other from the grid. In either case, the economics improve because the cost of both the electricity itself and the demand charges are greatly reduced.
The McKinsey article is more detailed than this excerpt.
It’s also explained in the McKinsey video below.