Speed limits for towing smaller trailers mostly derive from safety concerns about overloaded or imbalanced trailers being unstable at high speeds. A battery-only trailer with little or no cargo space, designed and certified in conjunction with specific tow vehicles, could easily be safe enough to operate at highway speeds.
I think the main reason why we don't see anyone seriously pursuing the battery trailer idea is that it would be an expensive niche product. It would have to be mostly a rental-only product, and offer few advantages over simply renting a more suitable vehicle.
Obviously a trailer would not be a clever idea, but Nio already has cars with swappable batteries, for short distances you could just install a battery pack which is maybe 20% battery and 80% empty space
It’s enough of a pain in the ass to swap summer and winter tires, and that’s something that (some) people only do twice a year. I can’t imagine people wanting to swap battery packs (either themself or by making an appointment at a service center) before and after every long trip.
Ideally they could just come to my home or workplace and swap the batteries out there while I am doing something else (if it is going to take longer than 30 mins)
Both upthread replies seem to evidence approximately the same level of effort to me; "It won't be faster" isn't wildly less effort than "what if it will be faster?"
Nio has fewer Nio battery swap stations operating in the entire world than just the state of New Jersey has filling stations (not dispensers, entire stations).
Nothing in the video above made me think "oh wow, that looks like that process will be a lot faster than filling up!" and several segments made it seem like there would be more time involved in just getting the car into and out of the battery replacement service bay than filling up takes. (Nio's claim of a 2.5-3 minute battery swap seems to be measuring only the swap time while the car is stopped in the bay.)
That's all before we consider the travel time to one of the stations (which is unlikely to be as close to your trip as a typical filling station because of the rarity of stations), time waiting for the car [or cars] in front of you to complete their swap (which if Nios ever became popular would likely be longer than waiting for one of the typically eight or more dispensers to free up at a filling station), nor to account for the "all long range batteries are out of stock at this location, because it's the Friday before Christmas and everyone is road tripping to visit family" NACKs that are liable to occur in a Nio-only battery swap system.
For me the killer line in the video that will make it hard for Nio to solve all of these is at https://www.youtube.com/watch?v=hNZy603as5w&t=270s : "Building these stations is incredibly expensive and it's no secret that Nio is losing a staggering amount of money right now..."
My point is, it may be interesting if it’s faster than filing up. Now, is it likely? Not at the moment, as you correctly pointed out.
Can I guarantee it will never happen? No. Hence my comment. It was not about stating what will happen or not, I don’t feel this type of prediction has any reliability. Millions of people smarter than me get it wrong every day, especially the very long term ones are almost always wrong.
Having done a long trip in an EV, in a very inhospitable location (the USA, without access to Tesla chargers), I'm not convinced there is an EV range/charge time problem. I think it's mostly in the minds of the public. Hence I'm skeptical that the changeable battery pack is a solution to any problem.
My experience was that you end up stopping to charge a bit more often than you'd stop to fill up gas, but factoring in stops for bathroom and food, it's really not a significant difference. There just needs to be more chargers (to avoid queuing for an open one), and chargers that are more closely spaced (every 50 miles like gas stations instead of every 100+ miles). Then today's EVs will be just fine for long trips. Not completely perfect, but perfectly adequate, to the point that it won't be worthwhile buying an ICE vehicle just to have it for long trips.
But it would be cool to just rent the extra 500km when needed :)