Perhaps the title is misleading, as I like small batteries too. What I really like is variety – different people have different needs, so I would like to see a wide range of battery sizes available on future cars.
A car with a small battery can be lighter (which can improve handling and acceleration), more efficient, and cheaper. For many applications – including as a second BEV – nothing more is required. I agree that small-battery cars are an important thing to offer. My only issue with small-battery arguments is that sometimes their advocates are arguing less for variety and more for the superiority of small batteries, i.e. “Why drag around all that extra weight when you don’t need it”.
Of course somebody always chimes in to advocate for big batteries, but I feel the big-battery argument is often too simple: a bigger battery gives you more range. A similar thing happens on these forums when a potential buyer asks “Is it really worth it to buy the bigger battery? That seems like a lot of money for only xx miles of range.” Range is indeed an important advantage to big batteries, but it is far from the only one.
Longevity
From battery surveys such as this, it is clear that the vast majority of battery degradation comes from miles traveled. To drive any given distance, a larger battery suffers less wear. That is because the largest factor in battery degradation is the number of charging cycles. Even “cycles” can vary, but for a rough estimate let’s compare a 30kWh car (similar to a Nissan LEAF) to a 100kWh car (similar to a Tesla Model S 100D), assuming each has the same battery chemistry and cooling and is driven the same number of miles. Let’s say the battery is expected to degrade to 70% after 1,000 cycles. And let’s use the EPA efficiencies for the LEAF and Tesla – the smaller-battery LEAF is more efficient (not just because of the battery; it is also a smaller car).
Using these numbers, a Tesla S100D’s 100kWh battery won’t hit 70% until 335,000 miles. Even at that point, the range will be 235 miles, more than twice that of the LEAF when new, so the Tesla will clearly still be usable by somebody, even if not the original owner.
However, the LEAF will hit 70% at 107,000 miles. At that point it will be down to 75 miles of range; still usable for some, but far fewer. If you try to drive it as far as the Tesla, even assuming degradation is linear, you will essentially have no range left by 335k miles.
This doesn’t argue for arbitrarily large batteries; but it does make a good case for ones that are at least reasonably matched to the expected lifetime of the vehicle.
Resource use and cost
It is clear that a small-battery car will initially cost less to build, both in terms of dollars and resources.
However, the average US car is pulled out of service around 220k miles. As noted in the longevity section above, around 107,000 miles a 30kWh car should hit 1,000 cycles a.k.a. 70% of original range a.k.a. “end of mobile life” in terms of energy density. While it is still possible to continue driving the car, to give it range to continue performing the duties it was purchased for (and avoid faster degradation on the less-capable batteries), it will likely need a battery replacement. This means you have now used the resources of, and paid for, a 60kWh car.
You are still ahead, but the 30kWh car will hit the 70% point again at 214,000 miles; at which point it will clearly be uneconomical to buy a third battery. While it is true that only 60kWh of money and resources were consumed, the LEAF is now at the end of its service life. The Tesla, meanwhile, will still have about 270 miles of range on its first battery and should be going strong, so the greater cost and resources put in to the car (as opposed to the battery) can be amortized over more miles.
Even after a battery replacement, with like-new range, the 30kWh car with 107,000 miles will have less than half the range the 100kWh car will have at 335,000 miles. This means the 30kWh car will have reduced utility, and so be less valuable on the used market – increasing the chances of it being retired early. And during its life, its owner is more likely to have occasionally obtained the services of a more-capable vehicle.
I am not trying to claim that a big battery costs less in the long run; there are too many factors to consider. Almost certainly it will in some cases and won’t in others; determining the relative sizes of those groups is an exercise for the reader. But even when the big battery costs more in the long run, having to replace the battery in a small-battery car (and still get less useful life) greatly reduces the savings of starting with a smaller battery, while forfeiting the other big-battery advantages.
Resource use and cost is not necessarily a large advantage for small batteries as some assume. For some applications (though not all, hence my interest in variety) a large battery is not only more appropriate, but cheaper in the long run as well.
Performance
If you have a large battery with 3x greater capacity, you can pull 3x the power out of it. More power in EVs mean fewer people will feel like they have to buy ICE performance cars, SUVs/vans and tow vehicles. While a small-battery EV can easily replace a Yaris, you need a big-battery EV to replace the ICE vehicles that really use a lot of petroleum.
Of course not everybody needs better performance (and the heavier, more expensive fuses and DC-to-AC hardware and possible degradation that comes with it). That’s OK, even if you just pull the same power, you can now pull it much longer and postpone entering a limited performance “limp” or “turtle” mode until very near empty. And you are putting less stress on the battery while pulling that equal power.
Or, you could also keep the power level steady, but choose a less power-dense battery, which might have an advantage elsewhere (cost, weight, volume, longevity, C-rate, etc).
Charging speed
ICE drivers fear that EVs have many disadvantages. Most of their fears are unjustified, but charging speed (while on a road trip) is a real one. While it is not as big a deal as many fear because there are many ways around it (PHEV, fly, rent, 2nd car, etc), not to mention that almost all drivers have limiting biologic requirements, it still behooves us to make charging as fast as possible.
While other factors are involved, the main limit to charging speed is usually the “C-rate”. 1C is defined as the power rate at which a pack is safely charged in one hour. So for a 100kWh pack, 1C is 100kW. The max C rate varies with chemistry, buffers, cooling, etc. Tesla doesn’t publish specs, but the max charge rate at Superchargers appears to be around 122kW, which is 1.22C. 122kW charging is nice (although of course it’s only for roughly the first portion of the battery, then it has to taper down as the battery fills).
But for a 30kWh pack, 1.22C would only be 37kW. True, the total time to fill the smaller pack should be roughly the same. But you only get 1/3 of the miles for the same time charging, and miles are the goal on a road trip.
At some point we may hit grid or other limits, but right now big batteries help a lot with reducing the time spent charging on a road trip.
Charging flexibility
While driving and looking for your next charging station, with a larger battery you are more likely to be able to skip a nearby charger, and instead charge at one farther away that may be faster, cheaper or have better amenities.
You will have more opportunities to leave a charging station you don’t like earlier and head off to the next one. Or maybe staying longer to grab a meal at this charging station will let you skip the next one.
You are more likely to be able to use 120V charging at home, and use the big-battery buffer to fill in on days that you don’t have time to replenish all of the previous day’s driving. Or if you have two BEVs and just one charger, maybe you can alternate which car gets charged each night. Or maybe you can still get to work even after forgetting to charge one night.
On an extended road trip, a larger battery allows you to replenish more miles while sleeping even with an L2 charger, helping to increase the travel time before the next charging stop and reducing the charging time for the day.
Having a bigger energy buffer gives you many more options.
Infrastructure
Long-range cars rarely need around-town or workplace AC charging, and need a lot fewer DC charging stations. You might need DC stations every 40 miles in a cold mountain range for a 30kWh car, but you could put them 3 times as far apart if you were positioning them for a 100kWh car. Extend this to a 2D grid, and you only need 1/9 as many DC stations for full coverage.
There are of course other reasons to have more stations than the minimum for coverage; but in large empty spaces with little electrical capacity, the significant flexibility in station siting is a huge advantage. It can also be a big advantage in a crowded metropolitan area where parking spaces and electrical capacity may also be difficult to come across.
Speed and HVAC
No matter what your battery size is, you can always choose to make your next charge at the end of your battery range and cut it close. A few people seem to make a sport of that. But with regular driving, this situation is far less likely to happen to the owner of a large-battery car.
While rare even for most LEAF drivers (partly because they generally self-select shorter trips), they are more likely than Tesla drivers to encounter situations where they have to slow down and/or turn off HVAC in order to make sure they can make it to their destination. Stories like that are why many ICE drivers fear switching to a BEV. It’s no fun for the BEV driver either; in addition to the temperature discomfort and the annoyance of having to drive slow, they may well be concerned about what happens if they don’t make it to their destination. Having extra battery buffer greatly increases the chances that you can travel in comfort at the speed you like – without concern.
EV Adoption Rates
Consumer Reports and the Union of Concerned Scientists did a study that showed that 25% of all car buyers could buy a LEAF and be perfectly satisfied with no changes in their driving habits. There really are that many drivers that have electricity available where they park, and NEVER carry more or go farther than a LEAF can handle. The LEAF’s market share, unfortunately, is almost 2 orders of magnitude less than that.
We have all heard that most trips are under 40 miles and so short-range BEVs can handle them, but that argument convinces, well, almost nobody. Survey after survey shows that range and charging time (both related to battery size) are the biggest concerns of potential buyers. The latest survey on this topic that I have seen by CleanTechnica says that even if you survey existing BEV owners, half won’t buy another BEV unless it has at least 220 miles of range.
More people will buy a BEV if bigger batteries are available! Whether they really need it or not, having a variety of large-battery cars available will help get us off petroleum.
I love big batteries, even when I don’t “need the range”
Small, efficient EVs are great, and not everybody needs a big battery. But if somebody questions your “waste” of a big battery, you can point out many benefits beyond being able to take an occasional longer drive without having to stop and charge.
My apologies to the Nissan LEAF
The Nissan LEAF is a great car that is well-loved by its owners. After Tesla, I believe Nissan to be the most serious about delivering EVs in quantity. The new LEAF will be introduced on September 5, and I expect it to have a big-battery option, which will make this blog look kind of silly for calling out the LEAF as a short-range car.
I also believe the new LEAF will continue to have a short-range battery option. I hope so, because they certainly have their place. I mean the LEAF no disrespect – I am only using it because it is the best-known example of a short-range BEV, which makes it easier to illuminate some of the less-appreciated advantages of big batteries.
TMC Member Chad Schwitters is a retired mobile software executive. He has been an EV driver since 2008 and a Tesla driver since 2009. Additionally, he served as Event Coordinator for the Seattle Electric Vehicle Association and as a board member for Plug In America.
Lead Image: FLDarren