# Battery trailer for long trip w/ EV? To simple?? **URL:** \ **Category:** Factual Questions\ **Created:** [November 6, 2014, 4:33pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898 "2014-11-06T16:33:10Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![HipGnosis](https://avatars.discourse-cdn.com/v4/letter/h/76d3ee/32.png) [@HipGnosis](https://boards.straightdope.com/u/HipGnosis)\ **Post date:** [November 6, 2014, 4:33pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/1 "2014-11-06T16:33:10Z")
Why can’t Electric Vehicles (EVs, aka cars) tow a trailer of batteries for long trips? It seems so simple and obvious… what am I (or the mfgs) missing? ---
**Author:** ![Lanzy](https://avatars.discourse-cdn.com/v4/letter/l/74df32/32.png) [@Lanzy](https://boards.straightdope.com/u/Lanzy)\ **Post date:** [November 6, 2014, 4:38pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/2 "2014-11-06T16:38:10Z")
or just have a really big battery you can tow and be connected to the whole trip? Might weight a ton or 2. Tow a running generator? ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [November 6, 2014, 4:38pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/3 "2014-11-06T16:38:59Z")
They’re very expensive, heavy, and turn your car into a rig that’s hard to park and drive in tight places. Smaller EV cars aren’t designed to haul heavy loads. ---
**Author:** ![Finagle](https://avatars.discourse-cdn.com/v4/letter/f/b19c9b/32.png) [@Finagle](https://boards.straightdope.com/u/Finagle)\ **Post date:** [November 6, 2014, 5:30pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/4 "2014-11-06T17:30:35Z")
It looks like the Tesla 85kwh battery pack costs about $25K and weighs 1000 lbs. If I were going to tow something that costly and heavy, I’d want to be able to waterski off the back of it. The idea is sound, but you get into the same diminishing returns you get when designing rockets. The energy in the car’s original battery pack gets used up faster because it’s towing the auxiliary battery pack and the same thing happens with the auxiliary battery pack. So you don’t double your mileage – maybe you get a 50% range increase at a considerable cost in inconvenience and expense. Tesla’s approach, as yet unimplemented, is simply to swap out the battery packs on long trips. On the return trip, you pick up your original battery. ---
**Author:** ![Emtar\_KronJonDerSohn](https://avatars.discourse-cdn.com/v4/letter/e/58956e/32.png) [@Emtar\_KronJonDerSohn](https://boards.straightdope.com/u/Emtar_KronJonDerSohn)\ **Post date:** [November 6, 2014, 6:39pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/5 "2014-11-06T18:39:32Z")
Off the top of my head I would suppose the added weight would affect efficiency toward a point of diminishing returns. Backing a trailer is different than backing a car without a trailer. Having a trailer limits where you can park, and parallel parking is much harder with a trailer than in a regular car (and an awful lot of drivers can’t even park a regular car.) Batteries like to be drained and recharged, and if you only use this heavy, expensive, cumbersome bank of batteries a few times a year you might only get a handful of trips out of the batteries. Tires, too. Really the best solution I have seen is banks of fast chargers installed at restaurants halfway between two sizeable cities. Drive a couple of hours, get some fries and a milkshake and use a little free WiFi for 45 minutes, then complete your trip. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [November 6, 2014, 6:51pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/6 "2014-11-06T18:51:06Z")
There was a company once that sold a gas powered generator intended to be towed behind your car, which could be used to start recharging the batteries when they ran low. Essentially turning your pure battery electric into a serial hybrid. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [November 6, 2014, 6:53pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/7 "2014-11-06T18:53:35Z")
I thought long ago the solution would be to tow a generator. You simply need to position the charger port (or one of them) Where the trailer could connect, plus appropriate safety configurations… also, the electronics to allow the car to travel and also have charger input. People tow trailers with the propane tank attached, why not a small generator? It would be very small, cheap, and relatively light, the gas tank refills at any gas station, and 90%+ of EV use is short enough that the trailer can remain at home. heck, the dealer could even offer it as an rental for longer trips. “intermittent hybrid”. ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [November 6, 2014, 6:54pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/8 "2014-11-06T18:54:06Z")
> [@Finagle](#): > > Tesla’s approach, as yet unimplemented, is simply to swap out the battery packs on long trips. On the return trip, you pick up your original battery. Or, use their supercharging stations which are spaced every 150-200 miles across the country, along the main travel routes. They tried to get the manufacturers of other electric cars to buy into it; as those cars have a maximum range of 50-85 miles, this request was met with resounding laughter. ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [November 6, 2014, 6:55pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/9 "2014-11-06T18:55:37Z")
> [@md2000](#): > > I thought long ago the solution would be to tow a generator. You simply need to position the charger port (or one of them) Where the trailer could connect, plus appropriate safety configurations… also, the electronics to allow the car to travel and also have charger input. People tow trailers with the propane tank attached, why not a small generator? It would be very small, cheap, and relatively light, the gas tank refills at any gas station, and 90%+ of EV use is short enough that the trailer can remain at home. heck, the dealer could even offer it as an rental for longer trips. > > “intermittent hybrid”. Congratulations, you’ve reinvented the Volt. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [November 6, 2014, 7:20pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/10 "2014-11-06T19:20:23Z")
> [@Ethilrist](#): > > Congratulations, you’ve reinvented the Volt. OK, stupid question, the Volt has a charger trailer available? Interesting. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [November 6, 2014, 7:29pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/11 "2014-11-06T19:29:30Z")
> [@md2000](#): > > OK, stupid question, the Volt has a charger trailer available? Interesting. It’s an onboard trailer. It’s just an electric car with a built in gas engine who’s job is to charge the batteries as needed. Why put it on a trailer? ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [November 6, 2014, 7:30pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/12 "2014-11-06T19:30:36Z")
On further reading, I see the Volt is a hybrid, like my Camry. Obviously, the whole “but it can only do 100 miles” problem is moot. OTOH, if you are driving a purely electric car, like the Leaf or Tesla - the problem still exists. You need to drive out in the country and back, 300 miles. Do you stop for several hours, find a friendly power plug, or do you take a trailer? Meanwhile, in regular use the vehicle is much lighter and smaller when not carrying a dead-weight gasoline engine, generator, and fuel tank if they are rarely used. I found a website discussing a 440-lb trailer. If a Nissan Leaf can save 440lb by not having a charging engine most of the time, why not? (Less parts, less maintenance) Of course, my concern about an electric in Canada is heat in the winter, while I imagine southern US drivers would have the opposite concern, summer air conditioning using up the power. ---
**Author:** ![busterpickle](https://avatars.discourse-cdn.com/v4/letter/b/258eb7/32.png) [@busterpickle](https://boards.straightdope.com/u/busterpickle)\ **Post date:** [November 6, 2014, 7:30pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/13 "2014-11-06T19:30:48Z")
> [@md2000](#): > > OK, stupid question, the Volt has a charger trailer available? Interesting. No, the Volt has a gas powered generator to keep the batteries in charge. However, the driveline is entirely electric. Unlike a Prius which has a electric/gas hybrid driveline. FYI: According to a co-worker, if the Prius hybrid runs out of gas, despite battery level, it will not run. A generator might do the trick. Assuming the car would accept the charging function while it was in drive mode. As the Tesla never intended for this, I assume that it won’t work, as you would want safeguards in place on overcharge occurrences as well as proper isolation of the battery, driveline, and charging. I also don’t think that a battery has sufficient power density for highway speed at distance. Sure, it’s awesome in the city with all the starts and stops but that’s where it ends. You still need a large amount of energy to go distance at speed, and that’s why it will be awhile until liquid fuels for cars are replaced. ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [November 6, 2014, 7:31pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/14 "2014-11-06T19:31:13Z")
> [@Finagle](#): > > Tesla’s approach, as yet unimplemented, is simply to swap out the battery packs on long trips. On the return trip, you pick up your original battery. I long ago did some serious design work on a car that could be built using then-current tech. A key element was a battery pack that slid in and out along the car’s “spine” - about where the tranny hump is in most RWD cars - and could be replaced in a minute or two at a recharging/swap station. I would expect at least some electric vehicles to standardize around a shared model like this in the next 10-15 years. It solves so many of the last-mile problems with EVs, especially small city and inter-city commute ones. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [November 6, 2014, 7:38pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/15 "2014-11-06T19:38:58Z")
The company I was thinking of with the towable generator is “AC Propulsion”. The towable generator, which I don’t believe they make anymore. I ran across it back in 2006: > **[AC Propulsion tzero | Long Ranger genset trailer](https://en.wikipedia.org/wiki/AC_Propulsion_tzero#Long_Ranger_genset_trailer)** > > AC Propulsion also built a portable internal combustion powered generator mounted on a trailer known as the Long Ranger that can be towed behind the car and feed power to the batteries during travel. The trailer uses a 500 cc Kawasaki engine with a 9.5 U.S. gallon (40 liter) fuel tank and achieved 30–35 mpg‑US (7.8–6.7 L/100 km; 36–42 mpg‑imp) in highway driving over at least 20,000 mi (32,000 km). It is rated at 20 kW (27 hp) DC output and can maintain 60–80 mph (97–129 km/h). The trailer incorp... The idea is still being explored by others, apparently: > **[Charge to go: The EP Tender portable EV range extender](https://newatlas.com/ev-charging-trailer/28513/)** > > While electric vehicle charging networks continue to evolve and expand, there is another approach to reducing range anxiety: taking the charger with you. The EP Tender range-extender system is designed to give an extra lease of life to EV batteries... BTW, the “serial hybrid” idea predated the Volt. I’ve always liked the approach over parallel hybrid. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [November 6, 2014, 8:20pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/16 "2014-11-06T20:20:27Z")
The problem with swappable battery packs is obvious - the quality of batteries can vary significantly with charge history and age. You’d almost need some arrangement where the batteries are all owned by a central company (car maker(s)?) who will accept any of their own battery packs as a trade for another of their own, with stations across the country. The car owner does not have to risk receiving a dud, they can always trade. Yeah, a serial hybrid makes more sense, you don’t need the additional transmission. In the extreme, you could have 4 motors in the wheels, and precise computer control as the AWD traction control. However, a gas motor still means you need to expand the frame to make the space for motor and generator, firewall for flame issues, gas tank, additional systems (starter, fuel pump, and all those other mechanical complexities). Removing the gasoline engine completely ahs some significant advantages, but severely restricts range and “refuel” time. ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [November 6, 2014, 8:34pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/17 "2014-11-06T20:34:36Z")
> [@md2000](#): > > The problem with swappable battery packs is obvious - the quality of batteries can vary significantly with charge history and age. You’d almost need some arrangement where the batteries are all owned by a central company (car maker(s)?) who will accept any of their own battery packs as a trade for another of their own, with stations across the country. The car owner does not have to risk receiving a dud, they can always trade. That’s exactly it. You’d buy the car and lease the battery pack, or some similar arrangement. Not a lot different from buying a car and then buying gas, really. ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [November 6, 2014, 8:47pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/18 "2014-11-06T20:47:36Z")
Tesla’s plan, last I heard, was that you had to either go back to the place that has your battery and get it swapped back in, or pay them a replacement fee for your brand-new battery. Might be a scam for people to take advantage of once their batteries start to degrade, if the new ones are cheaper this way than just buying one. The gigafactory may well be online and cranking out the batteries before we start to see degraded Tesla batteries, though, so that’ll bring the price down as well. ---
**Author:** ![TSBG](https://avatars.discourse-cdn.com/v4/letter/t/77aa72/32.png) [@TSBG](https://boards.straightdope.com/u/TSBG)\ **Post date:** [November 6, 2014, 9:38pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/19 "2014-11-06T21:38:02Z")
> [@electronbee](#): > > … FYI: According to a co-worker, if the Prius hybrid runs out of gas, despite battery level, it will not run. … Not true for my 2010 Prius. It has an “EV” mode, which will take you a short distance depending on charge, which I think is meant to help you limp to a gas station if you run out. ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [November 7, 2014, 12:03pm UTC](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898/20 "2014-11-07T12:03:42Z")
> [@Ethilrist](#): > > Tesla’s plan, last I heard, was that you had to either go back to the place that has your battery and get it swapped back in, or pay them a replacement fee for your brand-new battery. Might be a scam for people to take advantage of once their batteries start to degrade, if the new ones are cheaper this way than just buying one. The gigafactory may well be online and cranking out the batteries before we start to see degraded Tesla batteries, though, so that’ll bring the price down as well. It may well be a business opportunity though… loaner batteries You are driving along and need 100 more miles NOW… you swap out the battery… But they put the weight in the middle for stability so its a lot of work to swap it out … [Next page](https://boards.straightdope.com/t/battery-trailer-for-long-trip-w-ev-to-simple/703898.md?page=2)