Fast-charging batteries are a battery and its matching charger designed together, so that an electric three-wheeler fills up in fifteen minutes. Usually a charger and a battery are made by different companies, and the battery must remove the heat of charging with its own cooling. When both are designed together, the charger can also cool the battery, so the battery can safely take a higher current.
Here is a typical case. An electric auto-rickshaw driver in Delhi stops at a charging point for a tea break. The battery holds 8 kilowatt-hours and is at 10 per cent. The driver connects the charger. The battery's management system tells the charger, many times a second, how much current it can accept at this moment, depending on the temperature and the charge. In 15 minutes the battery reaches 100 per cent. That is 7.2 kilowatt-hours in a quarter of an hour, an average of about 29 kilowatts.
Two things make this possible. The battery cells are chosen to take high current without wearing out. And the charger cools the pack during the charge: it pumps cold water through channels inside the pack. Fast charging is supplied as direct current, as described in AC and DC.
Charging faster than a battery was made for shortens its life, because heat and high current damage the cells. So a battery that cools itself can take only as much current as its own cooling can handle. In a matched pair, the charger removes the extra heat. It also helps that the vehicles are of one kind, such as a three-wheeler used all day, so the design can be tuned for that duty.
A driver who earns by the trip cannot wait hours, so for this kind of vehicle, fast charging is an alternative to battery swapping. Swapping needs spare batteries for every vehicle, while fast charging needs only the charger. The same idea is now being used for intercity electric buses.