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Comment by lallysingh | Hacker News Reader

This took a few reads to parse. There are two kinds of batteries: (1) a low-density LFP that has a great lifetime, (2) a simulated manganese using Nickel manganese cobalt that has a poor lifetime but great density. The former cycles frequently for short trips, and the latter recharges it during the long ones.

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That's pretty clever.

It leverages the fact that most people make a large number of short trips, and a smaller number of long trips.

Also if it's modular enough, this design could allow replacing one or the other battery if the user does lots of short trips, or lots of long trips.

Also could let the manufacturer do market segmentation, e.g. a high performance model with no LFP, and both parts of the "high-performance" chemistry - and a base model that's 100% LFP.

Reminds me of how some SSDs do wear levelling, where they treat cells like they're one bit while the drive's empty and go up to four bits per cell as it fills up, with a speed penalty.

Considering that you can’t even change the 12v lead-acid battery in a BMW vehicle (ICE nor EV) without paying the dealer for programming, or some extensive hacking, I don’t hold out much hope for modular replacement.

You need more LFP to carry the weight of the manganese battery though (increasing cost), and all the extra weight can affect driving dynamics. Maybe both the cost and weight increase are minimal but that’s what came to mind. It’s a great idea though.

EVs already have far better driving dynamics than gas cars... doesn't seem like what designers should be optimizing for, or what the average consumer will care most about.

“Far better driving dynamics than gas cars”? No way. Go throw a BMW 3-series around some corners and compare to the Model 3 - you will feel the weight of the batteries. I would have said compare to a Porsche but that’s a different price range.

Note: I’m a big fan of EVs. I’m just saying that handling is one of their weaknesses until battery density gets a lot better.

The average people don't buy BMW or Tesla, they buy Honda CR-V. And they'll appreciate 500mi range far more than being able to take turns fast

Zero people drive 500 miles in a straight line on a daily basis though, so cornering ability is more important than 500 miles of range, especially when most gasoline cars (several diesels do) don't get that much range in a single tank. The biggest change for EVs is the ability to charge the car at home, though, so you wake up every morning with a full tank of "gas". An EV with only 50 miles of range would do great for most people if they had home charging given how many miles "most people" drive in a day.

I don't work for BMW (or Honda, or Tesla) though, so what do I know.

If people have to choose between being able to drive 500 miles with good enough handling and 200 miles with razor sharp sportscar handling the vast majority will pick the 500 mile car. Handling has long been good enough, most people don't get anywhere near what even their basic econobox can do.

Almost no public road driven at the speed limit would even come close to testing the cornering ability of a car mass produced in the last few decades.

Not even driving through Norway's or Switzerland's mountain roads has made me ever factor the cornering ability of a mass produced car into the equation. It doesn't matter outside of places you are putting a car's dynamics to its limits, the only place I know you should be doing that is on a race track.

You can’t get an EV at the same price as a ICE Honda CR-V, so that’s not an apples to apples comparison.

I dunno. Honda doesn’t offer an electric CR-V, but they’re coming out with the Prologue, which is slightly cheaper than the comparable Passport.

Passport: $43k Prologue: $48k - $7.5k tax credit.

Tax credit shouldn’t be included as it is inconsistently hard to get, and not available across all markets.

Checking Honda dealership near me, g there are configured CRVs that can be driven off the lot for $35k, without even considering that you can almost always haggle for good dealer markdowns on ICE cars but not EVs.

Ignoring tax credits, EVs were cheaper to comparable ICE vehicles when I did my calculation earlier this year after factoring fuel savings. But that is, admittedly, going to depend on the individual person's driving habits and fuel prices in their area, as well as their electricity prices. We drive a decent amount, our fuel prices are high, and our electricity prices are low, so we were close to the perfect combination of factors for EV. That is likely not the case everywhere.

For me, that ended up being ~$100/month which was decidedly more than the increase in monthly payment. And that's ignoring that the savings continue beyond the end of the payments.

It's also ignoring used vehicle prices. When I looked, and again, in my area, the difference in price between used vehicles was larger than in new.

Why not? Environmental effects of carbon aren't accounted for in the cost of an ICE

You're cherry picking data. Consider the original roadster and it's competitive again.

The one with less than 250mi of range?

Yes

I drove a BMW 3 series quite a bit (around Denver and then to Colorado Springs and back) and found the handling disappointing compared to my 3. Also, Googling “<model> weight” gives me a range of 3,862–4,048 lbs for a model 3 but 3,582–4,138 lbs for a 3 series. Since the battery pack is between the wheels, the weight balance of the model 3 makes it handle better.

You're comparing a sports sedan with a pretty normal sedan there. The fact that the model 3 can compete in the same league at all with the BMW has to do with the lower weight distribution caused by those batteries. It's not as simple as you're trying to make it sound.

Yes, to get more range you need more batteries, and those increase your weight meaning you need more batteries. But those increase your weight, so you need even more batteries. The tyranny of the rocket equation.

Not really specific to this dual-chemistry though, the same holds true for normal EVs and for gasoline-powered cars.

True, but the difference here is that the second battery isn’t even used most of the time, and if it was it would die quickly.

But is that really substantially different from somebody keeping their gas tank always at least half full, or making normal short-range trips with the long-range version of a Tesla?

Everyone already tried selling EVs with smaller batteries. The might be more efficient on paper but they don't sell. Turns out that trips people take once in a blue moon are still important to them, so a battery tuned to making that possible once in a blue moon sounds very useful.

> But is that really substantially different from somebody keeping their gas tank always at least half full, or making normal short-range trips with the long-range version of a Tesla?

A gallon of gas weighs around 6 pounds. A car usually has less than 20 gallon capacity. Keeping it half full would mean you keep 10 gallons which is 60 pounds. Even if you kept it full all the time, it is 120 pounds. That is going to be a lot less than any sizable battery ( theTesla Model 3 battery weighs around 1000 pounds).

It is a bit different from the rocket equation. The impact of weight on energy consumed per mile in a car is not particularly large. You can add hundreds of pounds and the impact will be negligible.

At least if you have regenerative brakes. Otherwise weight matters in stop and go traffic quite a bit.

Are there any EVs without regenerative brakes? As soon as that technology matured, given how much geopolitics is about energy, it's surprising to me we didn't mandate it's usage.

With EVs, they all have regen, but also, efficiency for range purposes primarily matters at highway speeds. There isn't a lot of stop and go there.

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