I'm not entirely sure that this question fits the primary purpose of this group BUT I have to say that I've long wondered why electric car manufacturers don't standardise on a battery format and devise some sort of unattended method of battery replacement.

I thought something that you drive the car onto and then the battery pack is ejected from underneath and a new one slotted in from underneath could work. From an engineering perspective, I guess the only risk is that when the battery is removed from the vehicle, the vehicle would be immobile until the new battery was fitted.

You could then re-engineer existing fuel stations to be equipped with some sort of charging rack in which incoming batteries would be installed and fully charged ones would be taken from.

I guess the biggest issue is that EV manufacturers have already established that they're going in another direction with the idea that batteries remain in the vehicle and are charged. Given that the format of the pins on the charging points vary wildly, the chances of getting manufacturers to standardise on a battery format are slim. I guess the thing stopping this is market forces, not engineering challenges. I guess that the only way that would change would be legislative changes from either one major or a small group of governments.

TL;DR:

This idea is old, like OLD (1890s), but so far nobody has been able to set it up in a financially viable way.

History

The steam car, the internal combustion engine automobile, and the electric car emerged as the main competing technologies in the late 1890s until the 1920s. The concept of exchangeable battery service was first proposed as early as 1896 in order to overcome the limited operating range of electric cars and trucks.

The concept was first put into practice by Hartford Electric Light Company through the GeVeCo battery service and was initially available for electric trucks. The vehicle owner purchased the vehicle from General Vehicle Company (GeVeCo, a subsidiary of the General Electric Company) without a battery and the electricity was purchased from Hartford Electric through an exchangeable battery. The owner paid a variable per-mile charge and a monthly service fee to cover maintenance and storage of the truck. Both vehicles and batteries were modified to facilitate a fast battery exchange. The service was provided between 1910 and 1924 and during that period vehicles using it covered more than 6 million miles. Beginning in 1917 a similar service was operated in Chicago for owners of Milburn Light Electric cars who also could buy the vehicle without the batteries.

Source: Wikipedia

Better Place company

Better Place was a venture-backed international company that developed and sold battery-charging and battery-switching services for electric cars. It was formally based in Palo Alto, California, but the bulk of its planning and operations were steered from Israel, where both its founder Shai Agassi and its chief investors resided.

[...] The company's financial difficulties were caused by mismanagement, wasteful efforts to establish toeholds and run pilots in too many countries, the high investment required to develop the charging and swapping infrastructure, and a market penetration far lower than originally predicted by Shai Agassi.

[...] The QuickDrop battery switch system would enable Renault Fluence Z.E.'s battery, the only vehicle deployed in the Better Place network, to be swapped in approximately three minutes at dedicated battery exchange stations.

Source: Wikipedia

A video of the process can be seen here: https://www.youtube.com/watch?v=qd0WPw3p2MQ

edit: as (I've just noticed that) @JamesJenkins has already pointed out:

Gogoro is everywhere in Taipei and now several other cities in Taiwan.

full disclosure; I'm not affiliated in any way and don't own one.

Spec sheet for electric scooter and battery:

• imperial units


• metric units

System (including batteries) is waterproof:

• IPX6, Above 30 mm:


• IPX7, Below 30 mm

Taiwan currently has over 1,000 swap locations, you pick a nearby site on your phone, "reserve" a pair of batteries and go there and swap them in a few seconds.

• 
  https://youtu.be/W34k0nrrDQA (regenerative braking at 01:40)


• https://youtu.be/Oa3Eht7_RJM


• 
  https://youtu.be/VD4s92gwlMY (power train details)


• 
  https://youtu.be/g_-PKSPbvpw (advertisement)

One possible solution is a flow battery. Electrolyte could be replaced in very much the same way as we refill a car.

The downside though is that the electrolyte is some kind of strong acid. You think spilling flammable petroleum products are a problem? Try spilling acid which will eat through your clothes, your leg, your car bodywork, the concrete floor...

It's still a viable solution. The engineering to keep the acid in and the rest of the world out is non-trivial though, so we'd need a really good reason to do it.

This is currently in use in Taiwan for scooters.

A record 20,915 new electric scooters were registered last year, nearly double the previous year's number. Consumers were drawn in by government subsidies, along with a quick and convenient battery exchange system devised by a local startup. Source

And

Yamaha and Gogoro have both proven to be powerful forces in the light electric vehicle industry. Gogoro has a line of highly successful scooters based on their battery-swapping technology, and Yamaha just rolled their four latest electric bicycle models into shops in the US.

Now the two companies have announced that they will be joining forces on swappable-battery electric scooters, leveraging the strengths of both players. Source

CC image that I was not able to load correctly

The problem with standarized, replacable batteries is with their size. In common electric cars, battery(-pack) is as big as the whole car:

I don't see the way to easily swap it to charged one on the battery gas station. It is possible to place different kind of batteries in, for example, trunk, but low placement of battery pack has additional benefit of lowering the mass center.

Honda apparently is working on charging-by-replacing batteries in their bikes (smaller batteries than in cars):

https://www.electrive.com/2018/11/30/honda-launches-pcx-electric-scooter-with-battery-swapping/

Not going to happen.

It is widely accepted that the best electric cars today are Tesla. While somebody could argue their frameless door windows, big external size, big wheels with practically no tire left, etc. are just for show and not for go, the technology in Teslas exceeds that of the technology in other electric cars.

So, let's take a look how Tesla uses batteries.

The batteries in Tesla are cylindrical cells, 18650 or 2170. 18650 has approximately 3 Ah of capacity, whereas 2170 has approximately 6 Ah. It watt-hours it's 10.8 or 21.6 watt hours, or in kilojoules it's 38.9 kJ or 77.8 kJ. A liter of gasoline is 36 MJ, so these figures correspond to about 1 or 2 milliliters of gasoline. So, if you are going to change these batteries, you will be changing energy 1 or 2 milliliters at a time. See the problem?

Ok, somebody could claim that best gasoline vehicles (=hybrid) are only 33% efficient, so in reality you will be changing energy 3 or 6 milliliters gasoline equivalent at a time.

These batteries in Tesla are hidden under the floor of the car, giving low center of gravity (thus safe and good handling), good behaviour in a car crash, huge electric range, a front trunk (frunk) where you can store stuff, etc. Although in theory the cells can be changed, in practice you don't do it. The Tesla cells typically last for the life of the vehicle, because you are using only tiny fraction of the cell capacities in typical driving.

Now, could you make the cells into larger multi-cell units? Yep, perhaps you could. In fact, Toyota has made the NiMH battery into a single unit. The trouble is that the tiny 1.6 kWh unit in RAV4 hybrid weighs about 70 kilograms and in this particular Toyota it takes some trunk space in the rear because it's not under the floor of the vehicle. Also, the units would differ in ideal dimensions between cars (and between different locations in the same car) to make use of the available space most efficient, making standardization difficult. Additionally, you need to lift the car up to change the cells in Tesla under the floor of the car.

Changeable batteries thus are not going to happen. The situation is similar to mobile phones. Making the battery difficult to change allows thin phones, which customers prefer. Making the cells difficult to change in a car allows low center of gravity even in a SUV, good and safe handling, crash safety, lots of storage space, long range, etc., which customers prefer, again.

In some manner, the cells actually are standardized in Tesla. They are very similar in size to common laptop cells, just use a slightly different chemistry that has been optimized for automotive use and for low cost. But, this standardized size means a single Tesla has a huge number of cells in difficult to access places.

However, there are several things that are going to happen, making electric passenger vehicles a reality:

• Battery cost will go down and size will go up.


• Quick charging will become more prevalent, allowing you to charge your car partially (not to 100% level, though, as the last few percent will be slow) while on a coffee break


• A secondary market will form for cells that have lost half or so of their capacity, and are thus not ideal for automotive use, but can be used to store wind and solar power in an electric grid for the rest of their useful life. Thus, the battery replacement will be cheaper than it is now, because you get a refund for partially useful cells.

There is a reliability problem with this idea that might not be obvious. To give a real-world analogy, four-engine planes have more engine problems per flying hour that two-engine planes, simply because there are twice as many engines for the faults to occur in.

If you split the "car battery" into multiple replaceable units, you multiply the reliability problems caused by bad connectors and bad individual units. If a problem like that leaves the car stranded somewhere, who pays to sort the problem out? The charging station doesn't "own" the batteries it charges and swaps, and neither does the car owner. So who picks up the cost arising from the faulty battery?

One good feature of conventional fuels is that they are a very standardized product - you can buy gas anywhere without even considering whether there going to be a problem with the fuel you just bought. You would need to make swappable batteries as reliable as that, which might be a hard engineering problem. Of course gas stations do sometimes screw up and have pumps dispensing the wrong fuel, but this is so rare and the consequences happen so quickly that it's clear where the blame lies.

Tesla at a point did feature a way to swap the entire empty battery assembly for a fully loaded one. The showcased process required only a prepared station the car would roll over and about 90 seconds later it could roll off with a full battery.

But then the abundance of free and fast superchargers offered a more compelling alternative and the project never really moved out of the pilot phase. Especially when considering that the ACTUAL process instead of 90 seconds took about seven minutes, was partially automated but partially still manual work (that can go wrong), required a pre-negotiated appointment and the car owner had to pay for it. On top of that, the vehicle did not recognize the new battery as such and continued to count the distance achieved with a supposedly single charge. Owners also were worried about the possibility of giving away their brand new but empty batteries for an old and worn out, albeit full one and thereby losing on maximum charge capacity, and thus vehicle price.

So probably all of these has lead to the state in which we are now, where the program is effectively dead, and based on the experiences no other vendor is rushing to implement their own version of it. In Musk's own words:

"People don’t care about pack swap. The superchargers are fast enough.
Based on what we’re seeing here, it’s unlikely to be something that’s
worth expanding in the future unless something changes."