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What are the advantages and disadvantages (technical, financial etc.) of having battery swapping system over charging stations for electric cars? As per my reading, battery swapping seems feasible for electric buses and 2-wheelers but not for cars. Is that really the case?

Also, is it possible for the battery to be housed under the bonnet instead of having it under the floor of the car so as to do away with underground swapping (like the one showcased by Tesla)? I know that the battery is placed there so as to lower the center of gravity. However, if there aren't any other significant benefits, can the aforementioned be done and battery swapping be made easier?

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  • $\begingroup$ How about paying for them and then what about expecting a full charge / distance and finding the pack that has just been installed has been gorillered and has a reduced capacity... $\endgroup$ – Solar Mike Jun 2 '18 at 10:58
  • $\begingroup$ I assume that a digital system is in place which let's both the car-driver and battery swapping personnel know the charge, capacity, identification number (for authentification) and all such details of the batteries. With this assumption, is it possible to not have an underground swapping system by changing the design of the car? My concern with the underground system is that it might fail in the rainy season. If the sealing is improper, water would get inside and a violent reaction might take place leading to an explosion. $\endgroup$ – user16060 Jun 2 '18 at 11:16
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This idea has been suggested often, but there's way more to it than you'd think. One big problem is that batteries are heavy, and there are multiple problems arising because of this. The main thing being the packaging in the car.

You want a decent range in a car, so the battery will be large and heavy. If you put it in the front, the car will be front heavy, and it'll be understeered. The front will break out in the corner. Same problem when putting it in the back, it'll be oversteered, which can be even more dangerous for ignorant drivers. You'll notice that a disturbed weight distribution causes bad driving behaviour in general, from a car.

Placing it too high will also cause problems, the car will dive under braking and accelerating, and it'll roll in the corners. Long story short, batteries are annoyingly big and heavy and awkaward things we have to get stuffed inside a car.

If you make people use batteries on exchange basis, you can only have a few standard battery sizes and configurations, or it'll be unfeasible. This means the battery will never be optimal for a specific car. And this is why exchange batteries aren't a thing. (yet)

Others often mention that different batteries will have a different quality, but I don't think this really matters. If you you have a lease contract, or if you pay per kilometer, the battery quality doesn't matter anymore. Bad ones will just be taken outof the cylce and be recycled.

It would be feasible if only a few different cars were used on the road, so the number of batteries exchange stations need to have in stock is also limited. Or, we'll have to wait for batterytechnology to advance a lot, so we can have a decent range with small and light batteries. Then the packaging would be less critical and standard battery sizes could be a solution. Until then, i don't think we'll see exhange batteries being offered at petrolstations.

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  • $\begingroup$ You said that having the battery in the front poses stability problem. So is it possible to distribute the battery between the front and the rear part of the car for stability? I guess that making electrical connection between those battery packs won't really be a problem. So would this work in terms of stability? $\endgroup$ – user16060 Jun 2 '18 at 17:29
  • $\begingroup$ @PMD That would be better yes. Still not ideal because the weight isn't at the center, but it's better. But it still can't be taylored to the specific car, and therefore it won't be able to use all the available space in the car. You'd end up with small batteries, and little room for luggage. The best option would be to have bridges(or slots in the ground) that you drive onto, exposing the bottom of the car, where the battery would be. A robot then could replace a battery with a fresh one. We'd have to get used to cars with higher floors though.. :p $\endgroup$ – Bart Jun 3 '18 at 13:02
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Advantages:

  • Minimal turnover time
  • Simple, standardized connection

Disadvantages:

  • Varying "remaining life" in batteries
  • Overhead of disposing of spent batteries
  • Needs standardization (or better, automation) of battery replacement

For example regarding varying age/use and recycling, I could start a business "recycling" batteries from BE (British Electricity) by putting them in my car and driving to the Cell station for replacement. I think that to minimize that kind of fraud, you'd have to "subscribe" to a particular vendor, and let them worry about swapping batteries with their competitors (kind of like roaming on phones, a premium service at first but eventually becoming an expected free service).

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  • $\begingroup$ Let's add to disadvantages, that the batteries need to be located in easily accessible sockets and mounted on a quickly detachable but strong standarized 'rack'. Fixed batteries may be placed wherever manufacturer deems them optimal for safety, balance, free space, and can be structurally secured to the frame in whatever configuration, in ways that don't necessarily make detaching them easy. Think problems of construction of devices running off AA batteries vs ones with built-in rechargeable battery: the latter is much more compact. $\endgroup$ – SF. Jun 11 '18 at 7:42

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