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There is so much confusion, misinformation and naive testing about this topic. I've only learned about this "80% battery thing" when researching EVs recently a

There is so much confusion, misinformation and naive testing about this topic. I've only learned about this "80% battery thing" when researching EVs recently and it seems to have been (maybe) spawned by the Nissan Leaf many years ago. And now it's appearing on HN seemingly once a week. What has changed? Is someone running an information(or disinformation) campaign? Blog or app to promote? I've not spoken earlier for fear of being downvoted into oblivion: I am sorry to say, but this 80% nonsense is just ... terrible advice and is 90% wrong. Like "skipping a daily coffee will let you retire 10 years sooner" wrong. (And all these lovely graphs I see thrown around are from poorly setup and poorly controlled tests using small samples or maybe even they're faked idk). To be horribly simplistic about it, the biggest factor in battery ageing is thermals. So if you want actionable advice on increasing the longevity of your battery (in the mobile phone context): Don't let it get hot, which means things like: * Take off that awful plastic insulator you call a phone case. (But we need phone cases) * Charge it slowly. Lower charge rate = less heat = happier battery. (But people love charging their phone in 1 minute) * Charge at human ambient temperature. (But on my bed, in the sun is easier) I guess those are inconvenient and poor sound bites. I'm sorry, but consumer devices (especially phones) have poor thermals and the environment they're subjected to sucks. That's just a fact of life (and economics and physics). Very simplistically, the only way "charge to 80% only" *might* be helping you is by keeping the battery cooler (In which case the above advice is much better).

appointment 3y ago
I think people are confused because of the advice to not charge above 80% on fast DC chargers, but that is about the exponential reduction in safe charging speed at high state of charge, not battery degradation (excepting old versions of the Nissan Leaf with bad battery management). If you fast charge to above 80% you are wasting your own time and the time of other people waiting to charge, so manufacturers usually quote fast charge times for a 10% to 80% charge, which is both more realistic and make the cars look better.
jve 3y ago
Tesla charges battery to 80%. The supercharger charges it there in less than an hour and manages thermals. And it charges very slowly at the end. Tesla battery lasts very well. Keeping battery between 20-80% is healthy. Your comment kind of implies that 80% charge is irrelevant, but the things you mention PLUS the discharge depth or how full you charge also affect the equation from what I gather. https://www.greencarreports.com/news/1110149_tesla-model-s-battery-life-what-the-data-show-so-far https://www.greencarreports.com/news/1110149_tesla-model-s-b...
- negative_zero 3y ago
  "Your comment kind of implies that 80% charge is irrelevant" I don't mean to merely imply that only charging up to 80% charge is (essentially) irrelevant. I mean to state that it is. What actually happens at around 80% is that the charging regime changes. It's nothing to do with "making the battery age less". A lithium battery has two charging regimes: Constant Current and Constant Voltage. Up to about 80% a lithium battery is charged with constant current => charge speed is limited by the maximum output current of the charger => bigger charger faster charger speed => happy customer. Above ~80% you switch to Constant Voltage. Charger now charges at a constant voltage and the charge current drops off following a log curve. The closer you get to 100% the lower the current => battery charges slower and slower the closer you get to 100%. This is a simple matter of physics and is the antithesis to "Fast Charging" which is why fast charging always talks about charging up to 80%. "but the things you mention PLUS the discharge depth or how full you charge also affect the equation from what I gather." Yes, depth of discharge (DoD) does affect battery ageing. But there's also a dozen other factors as well. Some affect the battery life more than DoD. So yeah don't waste your life trying to compile custom kernels or whatever to only charge to 80% :) Just help the battery keep cool with what I posted earlier. It's all you can do. Worry about other things in life :)
shmeeed 3y ago
Source?
- negative_zero 3y ago
  14 years in electronic products (consumer and industrial) including Multi chemistry battery management system (BMS) designs.

appointment 3y ago

I think people are confused because of the advice to not charge above 80% on fast DC chargers, but that is about the exponential reduction in safe charging speed at high state of charge, not battery degradation (excepting old versions of the Nissan Leaf with bad battery management). If you fast charge to above 80% you are wasting your own time and the time of other people waiting to charge, so manufacturers usually quote fast charge times for a 10% to 80% charge, which is both more realistic and make the cars look better.

jve 3y ago

Tesla charges battery to 80%. The supercharger charges it there in less than an hour and manages thermals. And it charges very slowly at the end. Tesla battery lasts very well. Keeping battery between 20-80% is healthy. Your comment kind of implies that 80% charge is irrelevant, but the things you mention PLUS the discharge depth or how full you charge also affect the equation from what I gather. https://www.greencarreports.com/news/1110149_tesla-model-s-battery-life-what-the-data-show-so-far https://www.greencarreports.com/news/1110149_tesla-model-s-b...

negative_zero 3y ago
"Your comment kind of implies that 80% charge is irrelevant" I don't mean to merely imply that only charging up to 80% charge is (essentially) irrelevant. I mean to state that it is. What actually happens at around 80% is that the charging regime changes. It's nothing to do with "making the battery age less". A lithium battery has two charging regimes: Constant Current and Constant Voltage. Up to about 80% a lithium battery is charged with constant current => charge speed is limited by the maximum output current of the charger => bigger charger faster charger speed => happy customer. Above ~80% you switch to Constant Voltage. Charger now charges at a constant voltage and the charge current drops off following a log curve. The closer you get to 100% the lower the current => battery charges slower and slower the closer you get to 100%. This is a simple matter of physics and is the antithesis to "Fast Charging" which is why fast charging always talks about charging up to 80%. "but the things you mention PLUS the discharge depth or how full you charge also affect the equation from what I gather." Yes, depth of discharge (DoD) does affect battery ageing. But there's also a dozen other factors as well. Some affect the battery life more than DoD. So yeah don't waste your life trying to compile custom kernels or whatever to only charge to 80% :) Just help the battery keep cool with what I posted earlier. It's all you can do. Worry about other things in life :)

shmeeed 3y ago

Source?

negative_zero 3y ago
14 years in electronic products (consumer and industrial) including Multi chemistry battery management system (BMS) designs.