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There is a Chinese company doing this. Tesla unveiled the concept years ago but decided not to do it. There are multiple reasons that battery replacement is no

by babesh 5y ago

There is a Chinese company doing this. Tesla unveiled the concept years ago but decided not to do it. There are multiple reasons that battery replacement is not as good as it seems. Charging stations can be built in more locations and more densely than battery swapping locations. This is because you need to store those batteries somewhere and there is more space and machinery involved in swapping. So you trade off queueing time for charging time. Charging stations are most likely cheaper to build and maintain because of the space and machinery requirements. A battery swapping station is more vulnerable to supply imbalances. Charging stations meet demand at charging rate. Charging stations can be more easily made universal. Unless you mandate a common battery form factor, that won’t be the case for battery replacement. This means that charging stations can scale with the whole EV industry. Swapping introduces inefficiencies to the car. You need at least a little additional structure which is weight. The below article does point to advantages but again not what may first expect: cheaper initial cost for car, off peak charging time. Also note the industry standards. https://www.cnet.com/roadshow/news/china-ev-swappable-battery-standards-approved/ https://www.cnet.com/roadshow/news/china-ev-swappable-batter...

woleium 5y ago
why not have both? I have an external portable battery pack for my phone, why can't I attach a portable rented battery to the tow hook of my car?
- babesh 5y ago
  Today’s EVs are in some ways a hack. The energy contained in the battery is far less than in a tank of gasoline. To achieve range, most EVs are more aerodynamic than your average ICE car. Towing a battery out back would be horrible for aerodynamics and thus horrible for range. Furthermore, EVs achieve good EPA ranges by doing better in city driving where they can recover energy via regenerative braking. They do worse at highway speeds since air resistance increases superlinearly with speed. Towing something bad for aerodynamics at highway speeds would be doubly horrible. Lithium batteries must be kept within a temperature range. Too hot and they combust because the liquid electrolyte is flammable. They generate waste heat when discharging. If you don’t get rid of that heat, your battery will combust. That is why EVs have heating and cooling systems for the battery. Your towed battery, if you are extracting power from it directly, will need that. Phones deal with too much heat by shutting down or throttling CPU speed. Some EVs have crawl mode but not for excess heat AFAIK. Just buy an EV with more range. I think the Chinese standards could allow for different amounts of energy contained by the battery. For example, you can use different battery chemistries with the same form factor (nickel vs iron). In other words, there are additional costs borne by an EV with a towed battery beyond what you would have with an external battery pack for your phone.
  - babesh 5y ago
    Oh, another tidbit of understanding has to do with the size of the battery. Volume grows with the cube but surface area grows with the square. Therefore, a smaller battery would be easier to cool or may not need any cooling. A larger battery would need it. An EV car battery is a magnitudes larger than your cell phone battery. It is supposedly why elephants have big ears. Cooling.
    - woleium 5y ago
      Interesting, thank you. :) I guess in the long term an induction lane on the highway would make most sense then.

by babesh 5y ago

woleium 5y ago

why not have both? I have an external portable battery pack for my phone, why can't I attach a portable rented battery to the tow hook of my car?

babesh 5y ago
Today’s EVs are in some ways a hack. The energy contained in the battery is far less than in a tank of gasoline. To achieve range, most EVs are more aerodynamic than your average ICE car. Towing a battery out back would be horrible for aerodynamics and thus horrible for range. Furthermore, EVs achieve good EPA ranges by doing better in city driving where they can recover energy via regenerative braking. They do worse at highway speeds since air resistance increases superlinearly with speed. Towing something bad for aerodynamics at highway speeds would be doubly horrible. Lithium batteries must be kept within a temperature range. Too hot and they combust because the liquid electrolyte is flammable. They generate waste heat when discharging. If you don’t get rid of that heat, your battery will combust. That is why EVs have heating and cooling systems for the battery. Your towed battery, if you are extracting power from it directly, will need that. Phones deal with too much heat by shutting down or throttling CPU speed. Some EVs have crawl mode but not for excess heat AFAIK. Just buy an EV with more range. I think the Chinese standards could allow for different amounts of energy contained by the battery. For example, you can use different battery chemistries with the same form factor (nickel vs iron). In other words, there are additional costs borne by an EV with a towed battery beyond what you would have with an external battery pack for your phone.
- babesh 5y ago
  Oh, another tidbit of understanding has to do with the size of the battery. Volume grows with the cube but surface area grows with the square. Therefore, a smaller battery would be easier to cool or may not need any cooling. A larger battery would need it. An EV car battery is a magnitudes larger than your cell phone battery. It is supposedly why elephants have big ears. Cooling.
  - woleium 5y ago
    Interesting, thank you. :) I guess in the long term an induction lane on the highway would make most sense then.