Car trip lengths tend to be bimodal, either short around town trips or long haul road trips. This leaves electric cars in an awkward spot where they support both types of trips poorly, either lugging around too much weight/cost on battery that doesn’t get used or figuring out how to deal with long mid trip recharging.
Rather than trying to build an awkward, one size fits all battery, why not make a more modular design instead?
I’m imagining building electric cars with a cheap, 50 - 80 mile range battery that’s designed for daily driving and around town commutes and then a trailer you can attach to the back of the car that has a 300 - 400 mile battery in it. The trailer hitch would include a built in charging port that would allow the trailer battery to directly power the motors. Once the trailer is empty, you could pull it up to any designated swap station and swap it for a freshly charged trailer in a few minutes.
This feels like it would fit the needs of a large segment of the population much better than the current model of EVs and at a much more affordable total cost too. And yet I don’t see any companies investigating this approach or making moves in this direction. Is there something I’m missing about why this isn’t a good idea?
I imagine something like at a highway rest stop someone could mount a trailer battery on the back (non wheeled, free supported by the hitch), and then drive with that battery pack specifically recharging the main battery as fast as possible. At the next rest station one could drop off the now depleted battery pack and be on their way with a fuller main battery. However the time to load it and unload it would have to be less than the time of a rapid charge.
The wheeled trailer seems more problems then it’s worth as many people would have difficulty in towing a trailer, especially backing up, though It could be simular to my first idea of a non-wheeled trailer, just on a highway and it’s main job is recharging your main battery ASAP and dropped off quickly down the road. You really don’t want to be towing another set of wheels if you can avoid it as that’s sure to take its toll on range. So a quick use of any trailer for a recharge of the main batteries while moving, then drop it off, seems to make more sense.
This may work with super capacitors for very rapid recharging and then use them to more slowly recharge the main battery.
Also induction charging on a highway on the upgrades, in the slow lane so the EV’s can drive slower than highway speed and get more charge, if you want to pass, even in a EV, you can in the left, but you won’t be getting recharged.
For anyone who is good a driving a trailer, swaps will be much faster (excluding any necessary paperwork that must be physically done on site); however, for many people this could be much, much longer because it involves precise backing to get the ball over the hitch, even if they don’t need to back up the first trailer to drop it off. Add that in & forget about it, there will be a whole new category of Youtube driver fails!
Backing up.
People will forget that their vehicle is longer; this will cause accidents when they go to change lanes & don’t remember that they need to leave extra room because their normal short car is suddenly longer.
Need longer parking spaces; there are times where we’ve had issues stopping at a rest stop because all of the longer truck/RV/trailer spaces are filled up. You’d need even more of these.
Most of the ‘regular’ charging stations I’ve seen are car length head-in style; try to use one of those & the trailer would be blocking the drive lane in the parking lot.
Cost/weight (CAFE hit, when some cars give you a can of fix-a-flat instead of a spare) for the manufacturer to install.
Logistics
Where do I store it when I’m not using it?
If a rental, I’d assume it’s like a car rental company - are they open early in the morning when I want to get on the road, or do I need to leave work early the day before to pick it up before they close at 6pm? Where does someone with limited parking (apartment, inner city, etc) leave it overnight?
How far out of the way do I need to go to pickup/drop off said trailer from either end (middle) of my trip? (personally, most of my trips aren’t city-to-city, but suburbs-to-rural)
Rental car/truck companies charge more for one way rentals that returns. How expensive would the mid-trip swap be?
Logistical issues with the rental company distributing their supply back to where it’s needed; this happens now with rental bikes/scooters but it’s much easier for one person to load a bunch of them in a van & drive a few miles to a different docking location in one city than hundreds of miles away. They’d probably need someone with a CDL to drive a bunch on a flatbed / new car carrier like trailer. CDLs are in short supply as it is right now.
I can drive a trailer. We rented a log splitter; it was tough to back up because it was so low & short that I couldn’t see it in any of my mirrors & therefore hard to tell if I was/not going straight until I was really out of whack. With a larger, enclosed trailer that I usually drive, one can see it so one can tell if you’re lined up or not by watching your mirrors.
I seem to recall having read something about EV batteries having to be tightly integrated into the chassis of the vehicle in order to provide sufficient bulk/ballast so that the vehicle wouldn’t tip over that easily when turning or when in a collision.
Because if the batteries were separated out from the car, then something would have to replace the weight, but if you’re just filling the car up with useless ballast then that would reduce the EV’s range, so why not let the battery handle both functions?
As for the benefits of towing auxiliary batteries when the EV already has a standard full-size battery, I think a “trailer battery” would impact aerodynamics negatively, but it may be worth it if distance is an absolutely critical factor. Otherwise, it would be simpler if the driver just takes more breaks for charging.
Cost of development. Current electric cars are the result of not that many years of focused development. The ability to add and remove batteries would not only require additional development of the battery trailer, but also changes to the car to put in a connector that let the car safely draw power from both the existing bank of batteries and this new one.
And most electric cars are now sold and used to users who focus on those around town trips, or whose longer trips can be done in stages covered by the battery, or who can use charging stations and fast charging stations to complete them. This hypothetical new, more expensive, model (expensive both because of new development and, at least initially, lower production numbers) would be competing with all of these more mature technologies, that are also still improving.
There’s also an opportunity cost in moving research and development resources away from improving existing EV technology and the many projects into new battery chemistries.
Some past and existing projects have already happened on a similar idea, that of the swappable battery. Some of the same barriers to the success of those apply to the towable battery, and the swappable battery also covers some of the benefits and has more work done on it.
Then again, I’m not an EV engineer, maybe they and the EV execs have some compelling reason I’ve left out here.
Others have answered the OP well, but I’ll add my own experience. I drive about 15k/year, mostly around town but also 10 or so out of town road trips, including 4 500-mile each way trips to SoCal from Phoenix. I’ve done this driving 3 ways: ICE car, ICE car with trailer, EV. I haven’t yet towed with the EV.
By far, the most taxing, slow, and inefficient means is by ICE car with trailer. It’s a pain. I’m always checking my mirrors for trailer issues, because they happen, and often can’t be felt or heard. In CA, the hwy speed limit is 15 mph slower than it is for cars and buses. It’s also the least safe mode and requires the most maintenance.
Next is the ICE car. I have to maintain an engine and transmission to keep it runnning, I have to visit gas stations every week or 2, and it’s noisier, which contributes to fatigue. On the upside, the trip to CA is faster, because there’s just 2 10-minute stops.
The EV is best. Almost no maintenance, quieter, and the first fill up of any trip is done at home, while we sleep. The trip to California is 40 minutes longer because it requires 3 stops of 20 minutes. OTH, I feel noticeably less fatigued upon arrival than when using the ICE car.
As an EV driver, I have no interest in the OPs system. I don’t want to be swapping in batteries that have been used and abused by who knows how many other people. I definitely don’t want to be towing anything and dealing with all that hassle.
That said, I would love there to be a small emergency battery that I could carry on longer trips, with like 20 miles of range on it, just so I could be sure never to be stranded. I know there are roadside assistance units for this, but they are too big and expensive at the moment. Hopefully as battery technology improves, this could become an option.
A Tesla Model 3/Y battery is a bit over 1000 pounds. I’m not sure if that is just the cells + connections, or if it also includes the armor. A trailer that can carry 1500 pounds is about 300 pounds itself. So the total weight to tow is going to be in the 1500 pound range.
1500 pounds to tow is nothing for a Silverado, but that’s the max towing limit of a Nissan Leaf, which is exactly the type of small battery city car that this plan is designed for. I would not want to be on a road trip where I’m pushing my car to the maximum of its ability the whole time.
I do like the idea of adjusting battery size for vehicle use, as there’s no need to carry 300 miles of range for a car that never drives more than 50 miles per day. That is probably going to have to be done at the time of purchase though, and it probably only makes sense for commercial and fleets where the vehicles don’t need to be too versatile. FedEx or UPS could have a bunch of 100 mile trucks that never go more than 70 miles per day, and then some others for longer routes.
The idea of swapping out car parts to eliminate waiting time goes back more than a century. J. Walter Christie, a fascinating inventor* who was far from a crackpot, tried to put it into use in 1909.
Christie now switched his energies away from automobile racing to developing his front wheel drive New York taxicab design. With benefit of hindsight, the taxi design’s importance came in large part from the fact that it incorporated a transversely mounted engine/transmission assembly, applying a basic architecture that would be greeted as revolutionary when applied by Alec Issigonis in the BMC Mini fifty years later. However, in 1909 the idea of a ‘conventional lay-out’ was less firmly rooted than it would have become by 1959, and for Christie the vehicle’s more striking novelty lay the fact that the entire “forecarriage”, incorporating all the key mechanical components, could be detached and replaced in “less than one hour”, so that the vehicle could stay on the road while the engine maintenance took place. The car’s radical lay-out was to necessitate the manufacture of many complex components in-house, and problems encountered subsequently by other manufacturers producing or finding a dependable universal joint make it hard to believe that the Christie vehicle was particularly dependable. Given the heavy steering resulting from the fwd lay-out and a published unit price in 1909 of $2,600, it is understandable that the denizens of the New York cab trade did not flock to buy the Christie taxi.
Others have attempted to incorporate the concept in various ways but the same objections always rose: they were too expensive, too complicated, too unreliable, etc. I remember discussions of battery swaps on EVs for a decade or two, in all sorts of ingenious ways, but they never made it to commercial use. That’s not to say that something of the kind will never be invented, because it’s got too much potential to alleviate EV anxiety, but we’re nowhere near there now.
I’ve found that the car’s estimate of how many miles are left can vary enough that I don’t always trust it. It’s not a huge deal, but I’ve had to make a couple of unscheduled stops because I thought I had the range, but actually didn’t.
Ask yourself how much your time is worth. Say your time is worth $40/hour. If this battery trailer only saves you a half hour then you would have to be able to rent it for $20 or less; if it saves you an hour then you would have to be able to rent it for $40 or less… And considering that people go slower with a trailer it seems clear for most people that this rental would not be financially worth it.
The swap stations would be designed for you to go highway onramp to highway offramp, no backing up required. For both ends of the trip where you’re navigating surface streets, you can still use your onboard 80 mile battery.
There is no toll on range since you can just load more batteries in the trailer to make up for the loss of efficiency.
You could engineer the swap stations so your car just has to be in approximately the right position and the trailer would use computer vision to automatically drop onto the hitch.
You could engineer it so that the trailer has backup cameras that get automatically piped into the car for changing lanes. Also, self driving is pretty good for highways these days and the self driving system could know when you have a trailer and account for that, leaving you not having to worry about the driving portion.
No, they’d be fully automated, like charging stations are now. You pull in, hit a button on a mobile app and it tells you what bay to drive into to drop off/pick up.
Unless your suburb to rural trip is more than 60 miles long, just use your normal battery, these are designed for 300 - 1000 mile long trips, where you’d pick up your trailer at a highway offramp.
You have a pair of them on either side of of a highway and, under normal circumstances, the flow is balanced. If the flow isn’t balanced, you can use discounts or even paying people to hook up a trailer and tow it to the next swap station down the road.
There were already electric cars released with 80 miles of range. They didn’t sell well because customers had range anxiety for long trips.
You could build small motors into the trailer so the deadweight is a lot less than the scale weight.
The point of this is not saving time, it’s saving money. The cost of a 300 mile range battery pack is ~$15,000, and the cost of lugging the thing everywhere you go is ~15 - 25% of your electricity consumption. You could save ~$10K and ~15% on your fill up costs if you slimmed it down to a 80 mile battery and used an aux battery whenever you needed 400+ miles of range. Additionally, you wouldn’t need to support all of the complicated mechanics for even increasing fast charging speeds as the “charging” happens when you swap trailers.
If you’re someone that only does 2 - 5 road trips per year, even if it costs $150 per trip to rent the trailer, you would need to do road trips for 15 years for the in built battery to be financially worth it.
The criticism I’m hearing that I feel has the most legitimacy is that driving with a trailer is significantly more difficult than driving without one. What if instead of a loose trailer, it was more like a truck bed with rigid mounting points to the back? It would effectively turn your Nissan Leaf into a Ford F150 for the duration of the trip, then you could go back to your normal economy sized car at the end of the trip. Most places in middle America are already designed to handle F150 sized vehicles so they’re not that much of an extra hassle.
As others have said, it’s a major hassle towing a trailer. Most people can’t drive a car competently and it’s a lot more difficult to tow a trailer. You to can’t really slam on your brakes or even slow quickly due to the trailer oscillating and pulling you out of control. I’ve got a small catamaran and a boat/trailer combination that weighs close to 9000 pounds fully loaded. You really have to be continually monitoring traffic ahead of you for potential stoppages and the gap between cars when you want to merge. Cameras do not really help an incompetent driver and quite often people won’t give you the room to merge even when you signal.
I’ve only driven on the freeway once when I was moving the boat and only drive on surface streets to launch the boat. I’ve seen people flip trailers because they were speeding on the way to Burning Man.
A (former) co-worker of mine solves this by simply renting a larger, ICE vehicle for long trips. At least for him, driving vacations were once/twice a year and he just rents an SUV or minivan for that week.
It seems likely the major rental car chains will keep a few large ICE choices available for many years. Maybe the OP’s idea will become more cost-effective in the distant future when ICE vehicles are rare though – it’s difficult to predict.
You can already save money with a Bolt or a Tesla 3. And they have plenty of range.
For most drivers, (not all) the OP’s suggestion is a solution looking for a problem. We have plenty of range for daily use and can stop in charge on the occasional road trip.
If you’re on the road all the time, then there are issues. I don’t think enough people do that routinely to support the infrastructure for the trailer idea. More range, and charging stations and faster charging is probably the way we’re headed.
Last night I ran over to Lowe’s with my Subaru Forester and brought home 11 bags of concrete mix at 60 lbs each. That’s 660 lbs of cargo, in addition to my body, so 880 pounds total. That was just under the max load limit of 900 lbs for this car. It’s not a heavyweight car – the somewhat more expensive Outback has a much greater towing capacity and I bet much greater car go capacity. Yet, 660 lbs is a whole lot of weight.
Wouldn’t an extra battery pack that fits inside the car be a good way to extend range for trips? Wouldn’t 660 lbs of battery give you quite a long range?
Yeah, and I mean, it’s not as if ICE drivers go around with two jerry cans strapped to the back unless we are heading out into the actual wilderness.
But yeah, what would be the incentive to make that set-up?
There would be ISTM a greater market incentive to make the fast recharging infrastructure and hardware interface more universal (can you imagine if every maker of ICE cars required you to use only their specific size and shape of pump nozzle at a specific volume per minute, or else you have to sit there all afternoon?)
