They need to come up with some standards for charging stations (ex: the plugs/voltage) and the battery packs. What would be neat is if they have a few different sizes, but for normal cars they would be small battery packs that can be lifted by one person, and they would slide in somewhere on the car and have a backplane. Most vehicles would have several of them in parallel. This could also make electric cars cheaper, as someone like me who mostly just sticks to driving in town I could get away with like 30km range. They could then have exchange programs that you can choose to use if you want, great if you're out of town. Or you could have spare battery packs on hand at home etc. They could perhaps even treat it like a rental, depending on the service you choose. Ex: you drop off your battery but choose the service where they keep it and charge it for you, and rent you another. You come back another time and get your battery back. Or you could do a full exchange. They could offer various options. These services would be ideal for people from out of town, for example. Normally you'd just charge at home after work. heck a lot of these stations could be practically in the middle of nowhere and run off mostly renewable energy, solar panels and wind turbine. The battery packs that are sitting on the chargers would literally be THE battery packs for the building itself. There would always be batteries on the go, with some that are fully charged. The station would pretty much run itself.
You could also buy extras to have at home on a charger that's ready to go. You can either plug the car in the charger or plug the battery in the charger. All the interconnects would be standard. Idealy, the charging logic would be in the battery pack itself, that would allow to only have 4 large terminals, 2 would be to power the car, and 2 would be for charging, the internal circuitry would then manage the balancing of each individual cell pack. Either make the voltage very standard, or have a standard comm port for the charger, that would dictate how much current is being put in so the pack knows how much to draw, but I'm thinking having a strict standard voltage would be best bet, then all the charger needs to do to dictate current is to lower voltage, ex: current limiting, then the internal pack knows to dial down how much it's drawing. At a charging station you would then have the option to pick the charge rate you want and pay more for faster, for example, and that would simply alter the current limit rate of the charger. Chargers on a certain breaker size such as 15 amp would then current limit accordingly to maximize use of that circuit. A
charger would really just be a power supply, it would be up to the battery pack itself to manage charging. This would even allow for different battery tech to be introduced in the future without having to change the charger infrastructure/standard. Would open a lot of doors.
Basically make a few standard battery pack formats where the size/connection and voltage is standard, the rest is up to the vehicle/battery pack. Could even have some NI-MH ones that are cheaper but much lower capacity.
Of course something like this would need to be very well engineered for safety too, if you have average people handling these. But it's not really any different than jerry cans. you're always going to have idiots filling their lawnmower with a cig in their mouth and having gas spilling everywhere and practically blow themselves up.