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Comment by Roark66 | Hacker News Reader

This may be so in Teslas that have quite robust heat management. It definitely doesn't apply to many other brands. Anyone who knows anything about lithium batteries and sees temperatures at which fast charging is done will not believe any of the longevity claims. It is up to 55C during charging and during subsequent driving on a motorway it can take half an hour for this temperature to drop below 40C (look up BYD Seal 1000 mile challenge on YouTube for an example - all above st 9C ambient).

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BYD started as a battery producer and still is one of the largest in the world - I can't imagine them not having considered proper thermal management for battery health. Especially since they have been producing electric buses since 2010, which, as utility vehicles, see way higher usage (=charges) than consumer cars.

I can imagine, and I can also imagine the buyer of those batteries stripping down "functionality" because of costs. So EV cars on the lower end could have higher peak temperature, because it's cheaper (i guess).

Is it a case of them not thinking about it, or did they think about it and figure that consumers would not pay for the increase in quality?

Plenty of engineered things could be "better" if price wasn't a concern. Most of this board can probably think back to a time where they had to leave long term value on the table because of short term costs concerns. It doesn't seem impossible to me that the engineers would leave some battery longevity (something that's hard to gauge for the consumer) on the table in pursuit of faster charging speed at lower prices (headline marketing items).

Doesn’t using an 800V architecture solve some of the heat problem? I believe currently the Koreans (Hyundai/Kia) and Porsche are the only major manufacturers using it. No surprise both can push nearly double as fast charging compared to 400v competitors.

The total pack voltage shouldn't really matter for internal heating, it's due to the cells internal resistance, higher voltage really only allow for thinner wiring than the crazy high current low voltage packs (especially important for chargers/contacts etc)

Internal heating is proportional to current. Higher voltage means lower current. Charging at the same wattage implies lower current.

So: higher voltage implies lower heating.

The cells need to charge whether they're in series or parallel. The efficiency they can absorb charge at high speeds without heating up is not primarily determined by how they're wired. You could wire 5,000 cells in series, charge them with 20kv at 4 amps, or wire them all in parallel, and charge with 4 volts at 20 ka. Each cell will produce the same amount of heat either way, they only charge with about 95% efficiency. Higher voltage doesn't really reduce the need for active cooling if you want to keep the cells under 40-50C.

Energy loss though resistance in the pack's internal wiring is likely a lot less than the loss due to the chemistry not being 100% efficient at absorbing (or delivering) charge without heating up. But it does allow for thinner wires to get max power out of the battery.

But I'm pretty sure the voltage seen by each individual battery is always the same, regardless of the distribution system voltage.

There should be less heating for higher voltages but if most if the heating is in the battery vs the distribution system then the higher voltages will not help much.

Also, if they make all wires smaller to save money and weight then there might not be any change in heating.

The current per cell is still the same. 800V charging just means that you put cells in series banks to achieve an ~800V module-level voltage. Current is reduced in the main charging cables, charge port, and pack fuse/contactor, but not in the individual cells.

Lucid uses a 1000V architecture.

I think the higher voltage allows them to charge more of the battery pack in parallel at a time.

And because of this, electric vehicle manufacturers should take note.

If only for a city only car that you mostly charge at home, don't do roadtrips with multiple fast charges in short period of time you may get away with passive cooling. And if you don't live in a hot climate. But those are too many IFs.

That describes our use case pretty well (for a 2-car household) and we’ve been quite happy with the 26K miles we put on our Nissan LEAF in MA over a coming up on 10 year period.

Charged at home >50% of the time and pre-pandemic on the 6.6kW chargers at work. I can only recall one attempt we made at a beyond single battery trip, using an EVGo DC charger at the mid-point. I can say it worked, but subsequent trips to that same location were in the ICE car, so take of that what you will.

The car is now 80+% charged at home and is a city/nearby suburb runabout (and used for more trips, albeit not more miles, than the other ICE/hybrid).

It still has about 85% of its original battery capacity, which means we charge it about once a week, which works just fine for us.

That also works for me for the second car. I also am awaiting Leaf delivery with 27k km on odo. however I did not expect battery to loose 15% of its capacity over 26k miles (which is 42kkm)

It is healthy to know how to maintain car battery. I will probably charge the battery to ~80% except when I need more range.

It’s also 10 years, which is a factor in degradation as well, not just cycles or distance.

It’s down 1 bar (of 12) and that was 2 years ago, so the 85% is estimated, but is within -0% to +4%. I have a LEAF Spy but haven’t checked it a long time.

Wasn't that how the Nissan Leaf's used to be setup, with passive cooling? I know it greatly affected their range in warm climates. I think they now switched to active cooling.

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