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Ask HN: Why don’t ELectric cars come with two batteries?

5 points by reacharavindh ↗ HN
I was thinking about electric cars, and their recharging times while on the occasional road trip. The solution seemed obvious in my head, but couldn’t think of a reason why it doesn’t exist already.

Say an electric car comes with a small sealed and fixed battery that gives up to say 100 miles of range. This is sufficient for most uses (to work and back, may be getting around the city, grocery trip etc). Another slot in the car that is usually empty may be “filled” with a battery along the highway while on a road trip. Reaching the end of range? - just swap out the “filled” battery.

This way, a customer gets to buy a cheaper car(smaller battery means lower cost). Buyer need not worry about getting stuck with a “aged” battery swapped with their good battery because swapping only occurs on the secondary battery that they don’t own.

Environment feels a little better - users don’t hoard Lithium batteries that they do t need all the time.

Businesses have a new way of earning money by selling subscriptions to such swap batteries.

The swap battery stations may be easily setup everywhere easier than full-on charging stations. The batteries themselves may be charged with renewable energy in huge factories and distributed to remote swap stations.

What am I missing?

17 comments

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shock
Batteries are heavy. A 100Ah battery weighs 25kgs. Cars have much bigger capacity batteries.
aristofun
Already tried and failed many years ago

https://en.wikipedia.org/wiki/Better_Place_(company)

reacharavindh
It doesn’t seem like the same as what I mentioned in the post. Also, if any company came to me and said they offered subscription based charging/battery switching in 2011, I’d have laughed them off as well. If I remember correctly the only plug-in cars to be found on the road were Prius and Chevy Volt. Both having the ability to fill up the tank for the road trip.

The market is ripe now with almost all major manufacturers adding electro cars to their line-up. I see this as an opportunity for these car manufacturers to easily compete with the ICE cars and capture the market because an EV with just 100 mile range can easily compete in price against the mass market ICE cars. I saw a Hyundai Ioniq 5 on a promo the other day, and boy does it cost > 50k EUR while essentially falling in VW Golf’s category.

muzani
I really liked the business model; it's a shame they failed. I think the reason they failed was that they expanded too aggressively. 5 countries for what's basically an infrastructure project.

By comparison, look at companies like Tesla and Amazon, they're huge, with a huge budget, but still avoid "locking out" the competition in other markets.

isbvhodnvemrwvn
I'd contest the "easily setup" bit in your post. You need a physical enclosed space with a lift or at least some mechanism to swap batteries which are likely to be 200-300kg each, it has to deal with rust and other shit that happens underneath the car. Then you likely need to move batteries around as demand changes. It's not at all like a charging station where the infrastructure is most of the time already there.
mrfusion
People like their cars to always be prepared for any need regardless of the frequency.

I even added four wheel drive to my last truck purchase because I got stuck once over the past four years. Not rational but I hate getting stuck.

mrfusion
Just to riff on your idea. I’d like to see them include a one time use 5-20 mile battery just to use in case you get stranded of out of charge.

Since it’s one time use I think we could use some really powerful chemistries that wouldn’t weigh as much. Aluminum something maybe?

LinuxBender
I think what you are looking for is advanced battery management. You can give the operator of the vehicle the perception that the battery is near depleted and have say 10% reserved to get to the next charging station. The owner should probably have the option to specify what "reserved" is based on their location and driving habits or by default the car could learn this and set it dynamically. Modern batteries can be monitored for age/capability/c-rating near real time with the current battery management systems even down to individual cells. It is up to the car manufacturer to implement this and do something with the information.

It is unlikely there would ever be extra physical batteries, as the battery pack would have to contain the same current capacity as the primary battery pack to meet the current rating of the motors. The battery pack makes up most of the weight of an EV.

toast0
> Say an electric car comes with a small sealed and fixed battery that gives up to say 100 miles of range.

> What am I missing?

A 100 mile battery is not small. Meaningful range extension would require a battery that is large and heavy and difficult to handle. Then you'd also need to quickly generate industry concensus on a shape and interface or there's too many variations and stocking becomes difficult.

Gustomaximus
Something like this they use for scooters in Taiwan?

https://youtu.be/6-ZCqeRSe3E

Could be useful to add some range quickly.

To be viable I'd think a couple key questions,1) How often do electric car drivers need this fast top-up? 2) How would this compare time to power vs pugging into a fast charge for 5 min 3) Could it deliver a significant vehicle cost saving reducing the main battery requirements?

Regarding the "charged with renewable energy in huge factories and distributed to remote swap stations." I would think getting the grid more green generally is the better and more realistic option.

reacharavindh
Yes, this ilmost exactly what I had in mind. If I could buy a "cheap" car today knowing that I could get extra range this way, I'd happily choose EV over an ICE without any anxiety. It would be nicer on the environment as well because not all cars are lugging around unnecessary battery they didn't need.

I seriously wonder why the same company - Gogoro didn't extend their reach to cars(at least partnered with one of the major car manufacturers eyeing the EV market).

perilunar
The Gogoro logo looks almost exactly the same as the Arduino logo.
dragonwriter
> Say an electric car comes with a small sealed and fixed battery that gives up to say 100 miles of range.

100 mile range electric car batteries are not small, on the order of a couple hundred pounds.

> Another slot in the car that is usually empty may be “filled” with a battery along the highway while on a road trip. Reaching the end of range? - just swap out the “filled” battery.

Okay, so this battery slot you are proposing keeping normally empty, but filling and swapping for road trips. This is presumably a not-small battery, like the main battery on a current Tesla, maybe a bit smaller to account for the nonswappable one. So probably something on the order of 1,000 pounds.

Not something you swap quickly, easily, or without special equipment.

perilunar
Alternatively, rentable genset trailers would be cool for road trips. Even better if they had a tray for extra luggage capacity.
reacharavindh
Now, that is also a great idea. I have never driven a car with a trailer. Is it very different driving dynamic than without?
ShakataGaNai
Yes. Depends on how big/long/tall/heavy the trailer is. If it's super small and light you might not notice much.

The heavier it is, the longer your braking time. When you start to stop, you can feel a heavy trailer behind you continue to "push" you along. Also if it's a heavy load and your vehicle doesn't have the power... it will be very very very slow to get up to speed.

If the trailer is long or wide, you've got navigate accordingly. At slow speeds, making turns, etc - you've got to drive like your vehicle is now potentially twice as long as it was before. Ever seen a semi make an absurdly wide turn? Yes, that.

ShakataGaNai
The problem is consumer views of "owning" things. Today if I go buy a new Tesla Model X Long Range, it's got a 400+ mile range. It's a brand new battery that'll be good for a decade.

However, if I go get the battery swapped out, then the "new" unit I get might be a battery that's 5 years old and is down to only 70% max life. Rinse and repeat. I never know what battery I get and it might significantly effect my possible range. But I paid for a brand new battery... so that's not fair.

A bunch of EV companies have looked at this and run into this problem of consumer sentiment. Also the system for swapping batteries needs to be automated and totally bullet proof. It cannot fail to swap a battery, ever. Which is not easy when you're talking about some sort of robot that needs to move a thousand pounds of battery.

Also what do you do with cars of different makes and models? The charging infrastructure is already challenging enough. Would you have a Ford battery swap station, separate from Tesla, separate from Rivian? If not that, you need to get every company AND every make/model of vehicle to be totally standardized.

For battery swaps to be really effective, it needs to be faster than charging - so almost as fast as filling gas. And have just as much range. So it can't be a 100 mile swap, it'd need to be at least 300. Otherwise someone driving slightly longer distance would need to be stopping to change battery every hour. Also it needs to be no more expensive than what consumers already have.

At the end of the day, battery swapping technology makes sense - but not for the average consumer. It's a great solution for fleet vehicles. Typically they are standardized single model of vehicle, the drivers don't care about the battery age (it's not their car), vehicle downtime matters (depending), and they have a central depot. Think about taxis for example, the depot can change the battery between driver shift changes.