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Comment by LeifCarrotson | Hacker News Reader

> So you are telling me they could of been build with smaller batteries and save money and the environment, but they were not...

If you charge and discharge a lithium ion cell from 4.2V to 2.75V, you might get 250 full cycles. If you stop charging at 4V and call that 100%, and stop discharging at 3.2V, you might get 2000 cycles before capacity is reduced.

Phone and laptop manufacturers prefer to burn the battery out in 2 years, car manufacturers want to sell bigger packs and are afraid consumers will rebel if a BEV needs a replacement battery at 100k miles.

Neither, for reasons unclear to me, allow the owner to make that decision.

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> If you charge and discharge a lithium ion cell from 4.2V to 2.75V, you might get 250 full cycles. If you stop charging at 4V and call that 100%, and stop discharging at 3.2V, you might get 2000 cycles before capacity is reduced.

Is there literally an almost 10x difference in the number of full cycles? Where can I read more about this?

The top end charge voltage is particularly sensitive, this is the most chemically unstable state of the cell charge cycle.

I really wish cell phones and computers came with an adjustment to max cell voltage. Cutting even 10% capacity can double your cycle life. Some do, but it's a hodgepodge and not standard.

https://batteryuniversity.com/article/bu-808-how-to-prolong-...

Thanks for the link. It is not clear to me if the resource is geared towards cell phone batteries or if it also applies to EV batteries, but I wouldn't be surprised if the trends apply to larger batteries as well.

Having said that, this resource does not seem to support the magnitude of the numbers in LeifCarrotson's comment that I was replying to. First, I did not see a relationship between voltage and Depth of Discharge (seems unlikely to be linear, especially given table 4), which is what the page seems to mostly talk about. Second, comparing 4.2V to 4.0V in table 4 suggests a 4x difference in the number of cycles, not a ~10x difference. Figure 6 also seems relevant and suggests maybe a 2x difference.

Something to keep in mind is that all of the tables are only trying to measure one thing and lay out the effect of the one variable. But in reality these can be mixed and matched for the desired performance characteristics. 10x is indeed possible by doing multiple things to extend the life of the cell.

Pull 4x from one table and 2-3x from another and it would probably put you somewhere in the 10x range. Though I'm not sure it would be strictly multiplicative.

>Neither, for reasons unclear to me, allow the owner to make that decision.

On Macs you can get something called AlDente which I use. Works quite well, free version https://apphousekitchen.com/

I mean, you can set your charge limit in every EV I know about

They know people will make horrible decisions and sue.

It would be trivial to implement a battery charge log.

“At this charge level, the battery will degrade to x kWh after y cycles”.

It's a bit more complex than that unfortunately. Depending on how long you stay at high charge level it will negatively impact the battery life. So someone charging at 100% all the time but discharging quickly might see a better cycling count that someone charging at 90% but staying there almost all the time.

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