charging phone to 80% prolongs battery life

[Jerry Adams]

https://www.cnbc.com/2019/06/12/apple-ios-13-will-improve-battery-life-with-optimized-battery-charging.html

Apple has a new feature that will charge phone to 80%, wait until just before it predicts you’re going to start using phone, then charge up the rest of the way.  This prolongs battery life.

Using that logic, if you just charged any phone or lithium battery to 80%, then stopped, that would also prolong battery life, actually even better.  If I start with a 100% charged phone it never goes below 50% or so, so just charging it to 80% would not be a problem.

When backpacking and charging phone from an external USB power supply, the last 20% (or 10%) of charging is less efficient so just charging to 80% would prolong the capacity of that USB power supply.

That article didn’t say how much this would extend phone battery, but they said this wasn’t an issue when people would replace their phone after 2 years, but now people are using phone 3 or 4 years – this charging strategy would help the phone last this longer period.

The problem is especially because if you charge your phone over night, it will quickly charge the phone, then maintain 100% charge with a trickle charge.  That’s what reduces battery life.  That would suggest another strategy to prolong phone battery life – don’t leave phone charging over night.  Charge to 100% then unplug it.

Using a USB power bank to charge while backpacking, if you let it trickle charge over night, that would just be wasted USB power bank capacity, you definitely don’t want to do that.

[Todd T]

I’m sticking with my gas-powered phone till the tech matures.

[Ken Larson]

Thanks Jerry will give it a try.

[Alex F]

Good to know! Was always wondering about that actually…

[David Thomas]

When I’m traveling and using my external battery pack, I usually charge to about 75-85% in part because that charging occurs much faster than the last 10-20%.  Good point about the efficiency of charging falling off as well.

Also, when I next have a charging opportunity, if my phone is at 100%, I can only charge my external battery.  Whereas, if neither are full, I can be charging two devices at once and be adding more total mWh’s in any given time.

[Jerry Adams]

I remember another thread from maybe a year or two ago.

If you let the lithium battery fully discharge, that reduces it’s lifetime.  Better to recharge when it gets down to 50% or even 75%.  Not that big a deal for lithium batteries though, compared to NiMh or NiCad batteries.

 

[john hansford]

I read somewhere to, ideally, keep your phone in the 40%-70% range of battery charge.

[Adam Kilpatrick]

I keep mine in the 40-80% range, have done for a couple of years. The exact percentages vary…few factors like exact chemistry of the battery, temperatures it experiences, rates of discharge and recharge, etc. I’ll let it go down to 20% occasionally, if I’m in a pinch, but no lower. And up to 100% occasionally, eg I know I’m about to go hiking.

I also deliberately use low amp chargers. Nothing over 1.0Amps. Charging too fast is also bad. One of my chargers is 0.7Amps which is beautiful. Lots of laptop USB outputs are less than 1.0Amps. Takes ages to charge, but, it doesn’t matter.

Anything that you can do to reduce the current draw on the phone helps. All those tips people already use (like airplane mode, using lighter versions of apps, etc) all help. Rate of discharge is important!

Temperature is also important, both during discharge and recharge and storage. Again it depends on the battery but about room temperature is best. Cold is really bad…keep your phone warm. Hot is also bad… your battery will perform really well but it will degrade badly within a few cycles.

If you happen to draw down your battery low…ALWAYS recharge it as soon as possible. Don’t leave it at low charge percentages, certainly not below about 40%. Otherwise it will start to degrade its cells, even if its off and not in use. Similarly, don’t store it at high percentages. The exact storage % and corresponding storage voltage depends….40-50% is about right though.

(do these things “wrong” and lithium based batteries don’t last long at all. I used to run a University drone program. As the drones are demanding, and we’d never take off with less than 100%, often running in warm temperatures, pushing flight time, rates of current draw, etc, a battery would often be dead after about 5-15 flights!)

 

[Jerry Adams]

that makes sense, good tips

is it okay if your phone gets cold (for example 20 F) but you warm it up (put in pocket) before turning on?

It was about 22 F on a recent trip.  I turned on phone and there was a weird blue triangle icon with exclamation mark.  I think it eventually turned on and I put it in my pocket to warm up.

I read that charging it when it’s cold reduces battery life

[Jerry Adams]

I’ve been trying to keep it in 40 to 80%, accidentally left it charging to 100%, not to worry.  At least I unplugged it and didn’t leave it trickle charging over night

I have a USB C charger.  Maybe I should switch to a regular USB that limits to 500 mA.

Too bad there isn’t a “preserve battery life” charging mode that stops at 80% and doesn’t trickle charge.

In that original article there’s a new mode that charges to 80%, predicts when you’re going to unplug it and charges up to 100% just before that.

In that article it points out that people used to get new phones every couple years because technology was changing so fast.  Now, technology is more mature so there’s less reason to get new model so people are keeping phone for 3 or 4 years.  At 2 years, batteries were fine.  At 3 or 4 years it’s more likely your battery will die so these battery preservation strategies are more useful.

I assume batteries don’t die hard, but just gradually lose capacity?  At some point the battery won’t last all day and it becomes inconvenient so battery replacement is in order?  As long as you’re replacing the battery you may as well just replace the phone?

[Roger Caffin]

As long as you’re replacing the battery you may as well just replace the phone?
Of course. Why replace the battery for $30 when you can replace the phone for $400? Think of all those poor Chinese workers who NEED you to buy a new phone.
Not to mention the hassle of moving ALL of your data over.

Cheers

[David Thomas]

As long as you’re replacing the battery you may as well just replace the phone?

I’ll stretch that expensive iPhone another for another year or two.

When my iPhones have gotten to reduced battery capacity, I take to carrying a $20 external battery with an iPhone charging strap that connects the two and usually a short, wide rubber band (like found around a bunch of broccoli) to hold them together.  Then, for maybe one trip into a store, I’ve got this double-sized package, but still usable package in my chest pocket.  20-30 minutes, it’s taken enough of a charge that I’m back to the phone itself.  I find it quite easy to deal with around town.  The annoying part is on a long day hike or overnighter on which I bring an external battery than I wouldn’t have otherwise.

[Jerry Adams]

I installed accubattery app

it beeps at me when it reaches 75% charge, that number can be adjusted

it would be better if it stopped, but I have to manually disconnect

I think that some phones have the hardware functionality to automatically stop charging at 75%

[HkNewman]

An Apple employee mentioned that to me when replacing an iPhone, but he said he couldn’t quite do it.  His wife lived for stopping their banks of phones at 70% though.  Different strokes for different folks, or as Lennon once sang “.. whatever gets you through the night”.

[Bruce Tolley]

Re: Apple
Is it a feature or a software workaround to make up for bad hardware design?

With the recent IOS upgrade, Apple has included a whole disclaimer about battery performance, batteries being consumables, etc etc etc.

[Rex Sanders]

Apple has several good explanations of iPhone battery management; they apparently work hard to extend battery life and lifespan while providing a good user experience.

iPhone Battery and Performance (long)
https://support.apple.com/en-us/HT208387

Apple makes an important distinction that Bob Gross schooled me on years ago:

“Battery life” is the amount of time a device runs before it needs to be recharged.
“Battery lifespan” is the amount of time a battery lasts until it needs to be replaced.

Also interesting:

A normal battery is designed to retain up to 80% of its original capacity at 500 complete charge cycles when operating under normal conditions.

In other words, if your iPhone goes from 100% charge to 0% charge every day, your battery will last about 500 days (1.4 years). If you go from 100% to 50% daily, your battery will last about 1,000 days (2.7 years).

The whole document is worth reading, especially for BPL iPhone users.

Others:

Maximizing Battery Life and Lifespan
https://www.apple.com/batteries/maximizing-performance/

Especially relevant are Apple’s battery temperature comfort zones for operation and storage.

Why Lithium-ion?
https://www.apple.com/batteries/why-lithium-ion/

Which explains charge cycles in more detail.

Finally, The Wirecutter (a pretty reliable source owned by NY Times) has great advice:

What You Should (and Shouldn’t) Do to Extend Your Phone’s Battery Life
https://thewirecutter.com/blog/what-you-should-and-shouldnt-do-to-extend-your-phones-battery-life/

Though slightly out of date on specific product references, battery technology hasn’t changed radically in four years.

— Rex

[Jerry Adams]

thanks, good info, I believe you started that previous thread about this

lifespan vs life – that’s the words I was looking for

“In other words, if your iPhone goes from 100% charge to 0% charge every day, your battery will last about 500 days (1.4 years). If you go from 100% to 50% daily, your battery will last about 1,000 days (2.7 years).”

and if you go from 80% to 30%, that’s 1/2 a cycle but you’ll get maybe twice as many cycles before you lose 20% of the battery capacity, so that would be 2,000 cycles.  Assuming you don’t over or under heat the battery and some other things mentioned in those links.  32 F to 113 F according to batteryuniversity.com, another good source of info.  Maybe 50 F to 86 F is better.  If you’re trickle charging a 100% charged battery it just loses battery lifetime for no reason.

 

[Jerry Adams]

at the risk of analyzing this to death

I noticed that if I use my phone for 8 hours during the day it consumes 50% of the battery

If I leave it on the other 16 hours without using it it consumes 20% of the battery

If I don’t charge it above 80% or below 30% I’ll get 1000 full cycles before the battery lowers to 80% of it’s new capacity

I’ll use 50% + 20% = 0.7 full cycles per day

1000 / 0.7 / 365 = 3.9 years before the battery lowers to 80% of new capacity

On the other hand, if I power the phone off for those 16 hours I don’t use it, I’ll save that 20% of battery capacity per day so I’ll only use 50% capacity per day = 0.5 full cycles.  1000 / 0.5 / 365 = 5.5 years

So, if I power the phone off for the 16 hours a day I don’t use it, it’ll last 5.5 years

On the other hand, if I have to replace the battery after 3.9 years or whatever, that’s only about $100 same day at Best Buy so not that big a deal.  It used to be that after 3.9 years that phones had advanced to the point I might just want a new phone anyway, but it seems like phone technology is maturing and there’s less reason to get a new one so often, maybe 5.5 years would be good.

Of course those are actually soft numbers – 3.9 and 5.5.  At year 3.9 the phone doesn’t suddenly die, it just gradually gets worse.  If I’m only using 50% of the capacity I won’t even notice it.

So, bottom line – try to only charge to 80% using that app that beeps at me unless I need a full charge.  May as well power it off when not using, like overnight.  But don’t worry about it, it’s not that expensive or inconvenient to replace battery if I want to continue using it years from now.

On the other hand, if I leave it charging all the time and when it’s hot or cold, I could kill the battery in a year.

 

[Jerry Adams]

just occurred to me – this is the only way for people to contact me – just leave it on all the time

too bad the charger doesn’t automatically turn off at 80%, and then run off the charger rather than the battery

[Diane “Piper” Soini]

Supposedly it is the same for the battery on my ebike. The problem is, if my ebike has only 80% charge, I can make only one round trip to and from work. If it has 100% I can make two round trips.

[Roger Caffin]

Could you pedal some more?

Cheers

[Diane “Piper” Soini]

My ebike is pedal assist. It does nothing for me unless I pedal. I can turn the assistance down really low. I once made 20% battery power make it home, but it was rough. I think when the motor is off it actually adds resistance.

[Hanz B]

Actually , I have an Comma eon that self drives my car and a lot of the battery gurus on my discord channel suggest that 70%-30% discharge range is optimal, along with some temperature thermal regulation. They seem pretty wise on this stuff so just thought I’d share. I’m clearly not backing this up with evidence but my eon (lithium smart phone cell) is going strong 1 year out by limiting the battery to that range.

[Jerry Adams]

The same thing can be true of a phone.  There are times when you want 100% of the capacity, like if you’re out hiking that could be a survival thing to not have your phone die.  If you need 100% then that’s what you should do.

I wonder how much a new ebike battery costs

If your ebike lasts 2 days, and it’s convenient to charge it in between, then you could charge it to 80% and make the battery have twice the lifetime.  Assuming it’s lifetime works the same way.  I wonder if letting it charge to 100% and leaving it on will hurt its lifetime like a phone.  Again, it’s too bad they don’t design the charger not to do that.

[Rex Sanders]

 

A couple of notes:

1. E-bike batteries run around $500. Not cheap.
2. I’ve owned a series of iPhones since 2008, and recharged to 100% every night. All of them lasted ~3 years without significant battery life (see above) issues. I usually replaced them because I “needed” new features on the newer models.
3. You’ll probably do more damage letting a battery drop to 0% and stay there for days or weeks out of neglect. Not a problem for most smartphone owners!
4. I recently replaced a 6-year-old inReach SE in part because the battery life was dropping (see #3), and because the inReach mini was half the weight. Six years was a pretty good run IMO.

I don’t sweat charging and battery life for recent devices with lithium batteries anymore.

I have a shelf full of power tool batteries on chargers in the garage. They’re all plugged into a no-longer-made Belkin surge protector with a remote switch. When I press the switch, the unit runs for 11 hours then turns off. Every week or two I click the switch. Batteries stay charged enough, but I’m not wasting power charging 24/7 or risking long-term overcharging. I haven’t seen any significant drops in battery life after several years of this scheme.

YMMV.

— Rex

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