So I’d read that draining a smartphone Li-On battery all the way down to 0% causes ‘deep discharge’ and permanent harm to the battery, such that phones are designed to emergency-shut-down once you get to 1%.
I’m curious what exactly causes harm at the moment of 0%, that is prevented by turning off the phone (or recharging) at 1-2%?
Electrolyte breakdown leading to internal shorting and thermal runaway:
Stranger
Ah, thanks. Unfortunately I’ve done it multiple times by now. Maybe I’ll get a Li-On replacement.
As I understand it, it’s not a step from 1% to 0% that makes all the difference. It’s that total life will get shorter the deeper towards ‘true zero’ one gets and the longer the battery stays there. For this reason almost all Li ion batteries have circuitry to create an artificial 0% above true zero. So when your phone says 0% the battery could actually produce power and may be more like ‘true 15%’, but using that last 15% would serious degrade the life of the battery. So manufactures set their artificial 0% point in a way that gives the battery life they desire.
But it’s just not hitting the low percentage, it’s also the time the battery spends at that low percentage that matters. So if you hit 0% on your phone or near it and recharge it right away it’s not a big deal, but if you leave it there for a while the battery will take a hit on it’s total life.
In your question there would not be much difference between 1% and 0%, but the problem with 0% is that it is possible for the phone battery to go below 0%, and that can start using up life pretty quickly.
Aside this is also true for 100% (but not as bad as true zero), that also gives a shorter battery life, and for this reason the 100% on the phone is not ‘true 100%’ either. To this many EV’s have the option to not fully charge it regularly, but just for longer trips if you can plan ahead.
Excellent question, and thus my cautionary tale of woe!
About 4 years ago, we bought 100 new Chromebooks for an experimental program where 100 chosen students (a grade level) would take an assigned machine home and back to school again every day. At the end of the year, they decided to abandon the project but, instead of collecting the 100 machines and integrating them back into the general population that receives daily use, they put the 100 machines in cart and stored it away … unplugged … uncharged.
Finally, a year later, they decided to use the machines again and, guess what? They had zero charge and could no longer accept a charge from AC. The batteries were totally dead on all 100 machines, which amounted to about $25,000 worth of inventory. Guess who was assigned the task of replacing all the batteries? Yep, me.
So, I have a regular charging program for all the machines we have in storage. Every 2 to 3 months, they get a full recharge.
Erm… that’s not so good. Try to store them around 40 to 50 percent charged. They’ll last a lot longer.
A lot of laptops have a charge setting specifically for this (sometimes it’s called long term battery life or something similar), so depending on your particular chromebook/laptop/whatever you might still be able to just plug them in every other month or so.
Yes as I pointed out 100%/near it is also harmful to total battery life. The sweet spot is at 40%, but practically 50% works well and allows some self discharging. The range 20%-80% overall is pretty good.
I have an app on my Android phone that reminds me to charge at 20% battery capacity and alerts me to take the phone off the charger at 80%. I’ve used it for years, and on my previous phone. I got 5 years out of that battery.
That explains something that had surprised me. My late first wife had a Surface Go tablet. Shortly after she died I got all her data off of it / her cloud but kept the machine intact. Thought I might want it as a backup or travel machine, and no incentive to wipe her stuff until I was actually ready to put it to use.
In the first few months I needed to fiddle with it maybe every 3-6 weeks for something of hers. It worked fine and I recharged it after each use. Eventually that intermittent use ended and it went in a drawer. Almost a year later I pulled it out to find it was stone dead but accepted a recharge & was usable again.
Almost another year later it was stone dead again which did not surprise me. Bbut to my surprise it would not charge, nor run on the charger alone. It was a brick, period. And not one worth replacing the non-replaceable battery on.
Since they literally die when abandoned and forgotten, perhaps their demise is due to the machine equivalent of a broken heart. LOL
I had the same thought. It was sorta poignant. Like this:
Ah, I love this! LOL
Yes, Dell laptops have this. I usually keep mine set so the maximum charge is between 70-90%, depending on if I have an upcoming event where I need more battery power. At almost three years old my current laptop still shows 0% battery degradation.
I have 60 laptops that I only use two months out of the year. They are currently four years old. So far the battery on three or four of them has completely died. They all go into storage with 80% battery, because they were plugged in while used, and that’s where the max charge is set. The odd thing is 10 months later when I pull them out the charges range from 0 to 50%. The 0% ones will give an immediate error about the clock being reset and all of the BIOS settings reset to default, and others act like I could have just turned them off yesterday.
Google phones can do a thing they call adaptive charging. If you have an alarm set, and plug the phone in at night then it will charge at full speed to 80%, and then slow charge to 100%. It will also delay charging the rest of the way to 100% in order to time being done charging shortly before the alarm is set to go off.
Google’s claim was that charging to 100% wasn’t a problem, but that the excessive heat produced fast charging from 80-100% was the real killer, so originally the adaptive system just fast charged to 80% and then slow charged to 100%, as long is it would finish before the alarm would go off. Otherwise it would fast charge the whole way. Because phones would typically reach 100% long before the alarm, people thought it wasn’t working, so Google added the delay to get to 100% closer to the alarm.
As @kanicbird mentioned, the more you discharge your battery, the more you shorten its life. In a couple of engineering design classes, I often trot out a figure similar to this one, showing that recharging the battery before it is discharged too far can keep the battery going a longer time:
What’s kind of interesting, although there are several different battery chemistries used through the years, they seem to be at least somewhat similar in their characteristics. They generally don’t “like” deep discharges. And they don’t like high temperatures.
I seem to remember NiCad equipped devices - mobile radios for example - used by gazillions of local, state, federal agencies, had a problem sometimes referred to as “memory”, where eventually the current capacity would be almost zero, ironically enough by keeping the device on the charger all the time and never being utilized.
It should be noted that 0% and 100%, and in fact every number in between, is completely fictional. It is entirely up to the manufacturer to choose where those boundaries lie.
There are competing interests when it comes to setting the range:
So there is some balance between the two, and the decision is different between, say, a phone vs. electric car. The EV battery is more expensive and so the endpoints are set more conservatively. A phone will take more damage when drained to zero than a car will, just because the car has its zero point set well above where there is actually no juice left. But phone battery replacements are cheap and people replace phones more often than cars anyway.
As it happens, the middle points are also fictitious. Lithium batteries in their various forms have a very flat voltage curve in the middle of the range. That makes it hard to measure capacity, because typically voltage is all you have to go by, and if everything in the 30-70% range is at almost the same voltage, you have no information. So what battery controllers do is measure how much energy was drawn from the battery and predict the remaining capacity from that.
Eventually the battery voltage will dip, so the controller can use that to calibrate its routines. But for the middle range it’s mostly predicted. And if you never discharge below 50% (say), the calibration can get out of whack and show you the wrong figure.
The facts stated above about battery wear at the extremes, and particularly letting it go dead, are certainly true and borne out by evidence. Anecdotally, though, I will say that if it does happen, depending on the specific battery design there’s probably no need to fret. I’ve had it happen to my phone and my Kindle a couple of times, and they still work fine. If battery life has been reduced, it’s not significant enough to notice.
The KIndle was interesting. After leaving it unused for awhile, I found the screen displaying a giant exclamation mark with a lightning bolt below it, sort of a last-gasp cry for help before it died (the Kindle of course uses e-ink which doesn’t require power to maintain an image). And dead it was. When I plugged it in to the computer’s USB port, nothing happened – no device was recognized, and there was no “charging” screen. It actually took several minutes before it came to life. And it clearly had been in a total no-power state, as my list of books which I keep in “most recently read” order was replaced by an apparently random sorting, and it didn’t work properly until I tweaked a few things. But it still works fine.
I’m now reminded that I have a laptop that I rarely use and an older one that I almost never use but that has useful stuff on it. I should attend to those and charge them up about halfway.
With older laptops you have the additional factor of spinning mechanical disk drives. Which may or may not power up after a long sit. Now is the time to get all the data you want to preserve off those things and onto someplace newer and safer.
Good advice, but being a techno-nerd, I long ago replaced the mechanical HDDs on both those laptops with SSDs. But a good point nonetheless – the SSD on the newer laptop is a modern Samsung Pro, but the older one has an ancient SSD where I actually had to flash a new firmware update to get it to work reliably! 
I’m glad this thread reminded me to look after my batteries. I just tried out my oldest laptop, which it now occurs to me I haven’t used in at least three or four years – the last time I used it was to format a microSD card since that’s the only computer I own that has a card slot.
With comical optimism, I pressed the “Power” button before plugging it in, and of course absolutely nothing happened. I plugged it in, it powered on, but the battery status showed 0% and “not charging”. It remained that way for about three or four minutes before it started to show “charging x%”. Good thing I saved that one before it was too late!
ETA: Currently at charging and 7% – it’s alive!