# charging percentage, capacity, and extending cell phone battery life

#### Poppy

##### Flashaholic
I have a economy Asus phone that shows battery charge %
When charging it, it takes about 2 minutes of charging to raise the percent charge 1%. (I am rounding numbers)
But when it gets to about 90% charged, it takes longer, maybe 4 minutes for each 1% increase in charge.

I assume that there is more capacity (watts) in the 90-100% segment of charge, than there is in the 80-90% segment of charge, because the voltage is slightly higher in the 90-100% charge segment. But is it significant?

I almost always have the ability to charge my phone, either with a wall wart, in my car, or from a power bank.

Please give me a strategy to extend/maximize the battery life. It doesn't have a replaceable battery. I'm thinking that it is better to NOT fully charge it, but rather stop at about 90%.

During the day, I put it on charge multiple times 10-20 minutes at a time, for example, I plug it in and out of the car charger as I run errands. I try to keep it above 50-60%.

Poppy

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#### parametrek

##### Enlightened
Yes, you are correct. But Li-ion doesn't really have a "full" charge. They can always be taken to a slightly higher voltage, hold a little more power and decay even faster. More at Battery University: http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

Take a look at table #4, that is the charge graph. Discharge and temperature matter a lot too. Everything makes li-ion wear out.

Good electronics will limit the charge already for you. Though offhand I don't know of anything smaller than an electric car that limits charging like that.

Edit: Whoops, misread a little. There isn't more power in the 90%-100% area. The charge current slows down though.

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#### Poppy

##### Flashaholic
parametrek,
Thank you for pointing to that link.

A few years ago I read many articles at that site, but haven't returned. Back then their LiIon info was a bit lacking, and confusing. They updated that page...

<snip>
the depth of discharge (DoD) determines the cycle count of the battery. The smaller the discharge (low DoD), the longer the battery will last. If at all possible, avoid full discharges and charge the battery more often between uses. Partial discharge on Li-ion is fine. There is no memory and the battery does not need periodic full discharge cycles to prolong life.
<snip>

Also they state: "
In terms of longevity, the optimal charge voltage is 3.92V/cell"
-----------------------------------------------------------------------------------------------------------------------
So I guess that if I keep it between 50% and 80% charge, most of the time, and don't use a fast charger, that should maximize the life of my battery.

#### terjee

##### Enlightened
Sounds like you've got this covered, but I just wanted to add in that dropping the voltage too low, is worse than fully charging. If you find yourself running past 25% capacity when you're using it, I'd rather recommend you fully charge it.

While it's true that it's better to charge to 90% than 100%, the difference isn't staggering. Okay, so in 2 years you might have 92% capacity left, rather than 90%, but is it really worth keeping an eye on when to interrupt the charging for those two years, for such a minor gain? (I invented those numbers to illustrate the point).

Enjoy your phone, try not to discharge too low on a regular basis, and don't stress too much over it.

#### BringerOfLight

##### Newly Enlightened
While it's true that it's better to charge to 90% than 100%, the difference isn't staggering. Okay, so in 2 years you might have 92% capacity left, rather than 90%, but is it really worth keeping an eye on when to interrupt the charging for those two years, for such a minor gain? (I invented those numbers to illustrate the point).
Only charging to 90% (usually done by charging to 4.1V instead of 4.2V) generally doubles cycle life. E.g.:
http://www.powerstream.com/lithium-ion-charge-voltage.htm

There are plenty of phones with batteries that are close to dead within 2 years.

#### Poppy

##### Flashaholic
Only charging to 90% (usually done by charging to 4.1V instead of 4.2V) generally doubles cycle life. E.g.:
http://www.powerstream.com/lithium-ion-charge-voltage.htm

There are plenty of phones with batteries that are close to dead within 2 years.
THANK YOU! BringerOfLight! :thumbsup:

That is exactly the information I was looking for.

Battery University stated that the optimal charge is 3.92 volts. And the chart that you linked to shows that at that voltage, one could expect about 7 times as many charge cycles.

I won't stress if I forget and charge it to 100%, but going forward, if I note that it is above 85%, I'll pull the plug.

#### markr6

##### Flashaholic
I typically charge my iPhone when it's around 50%; I just never use it much on a typical day. It may take 2 days to get me down to 50% from 90% or so. That's also where I stop charging it. I don't stress over it, but try to catch it around 80-90% then unplug it.

I'm still using an old 9+ year old flip phone as an alarm clock. It holds a charge for weeks, but of course I'm not using it much (standby plus a few seconds of alarm every morning).

#### StarHalo

##### Flashaholic
- The cell phone battery meter is a dark art; don't trust any reading below 25%, assume 25% is empty where possible. The top 5%/above 95% is usually more like 20%.

- It will always come down to convenience vs longevity. Plugging in your phone overnight and having it at 100% in the morning is very reassuring, especially if there is a power outage, or in the case of Android/Windows phones, some mysterious process turns out to have been running in the background.

- The speed/amperage of your charger also adds to battery wear; the usual 1A charger is very gentle with the battery, so long as you're willing to wait many hours for a charge. It sounds doable until you're having a hectic day and there's the possibility of using the 2.5A charger to get ~25% in ~20 mins.

- Will you still want this phone in two years? You can make a case for keeping it nice for yourself, but know that even in flawless showroom condition, it will by then be worth less than whatever you use to charge it (the value is determined by the condition of the screen, not the battery,) and won't be compatible with some apps.

#### Poppy

##### Flashaholic
- The cell phone battery meter is a dark art; don't trust any reading below 25%, assume 25% is empty where possible. The top 5%/above 95% is usually more like 20%.

- It will always come down to convenience vs longevity. Plugging in your phone overnight and having it at 100% in the morning is very reassuring, especially if there is a power outage, or in the case of Android/Windows phones, some mysterious process turns out to have been running in the background.

- The speed/amperage of your charger also adds to battery wear; the usual 1A charger is very gentle with the battery, so long as you're willing to wait many hours for a charge. It sounds doable until you're having a hectic day and there's the possibility of using the 2.5A charger to get ~25% in ~20 mins.

- Will you still want this phone in two years? You can make a case for keeping it nice for yourself, but know that even in flawless showroom condition, it will by then be worth less than whatever you use to charge it (the value is determined by the condition of the screen, not the battery,) and won't be compatible with some apps.
I haven't paid close enough attention to track at what percentage it drops most rapidly with use.
My phone does seem to drop pretty rapidly with use. I THINK the bottom 30% drops like a rock.
I'm not sure, I think the top 5% drops as quickly as any other 5%.

I have 1 and 2 amp charges in the car. I'll use 2 amps for up to 70% and 1 amp beyond that. My phone came with a 1.35 amp charger. Charging at 1 amp takes a long time. The phone sometimes reports how much time it estimates it will take to charge, and sometimes on the 1 amp setting it reports 10 hours.

Will I want the same phone in 2 years? I don't know... this one is limited in RAM. Last year or so, I recall my son being frustrated with his phone because the battery wasn't holding enough charge, and he wasn't eligible for an AT&T upgrade yet, and or he was waiting for an upcoming new phone, not yet released. Where ever he went he carried a power bank with him. I have 8 or 10 of them, and they are in constant rotation. He got his new phone about 6 months ago and it has the fast charge capability and he has the fast chargers to go with it. He still carries at least one of those 6600mah power banks in his EDC bag every day.

I'm rarely more than 100 yards away from my car. My USB power-port is hot all the time, with or without the key, and I always have a fully charged 6600mah power bank in there. So I am not concerned about a dead phone, during a power outage.

Using the 2 amp charger, it seems to take a little less than 2 minutes of charging to gain 1% of battery charge.
My phone does not have the fast charge ability where it will accept 9 volt 2 amp charges until it reaches 60%, so those smart fast chargers, will drop to 2 amps 5 volts for my phone, regardless of its percent of charge.

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#### StarHalo

##### Flashaholic
Don't forget battery cases; don't know if they make them for your model, but adding a battery case to my iPhone adds 150% capacity without carrying anything else, very handy.

#### Poppy

##### Flashaholic
Don't forget battery cases; don't know if they make them for your model, but adding a battery case to my iPhone adds 150% capacity without carrying anything else, very handy.
Thanks StarHalo

It was a BIG adjustment for me to carry a smartphone vs a flip-phone, due to the size.

I don't know if they make battery cases for my phone, its an Asus Zenfone 2E, which is, I guess, the economy model. It is possible they make it for the 2, and that it would fit the 2E. But I don't need to go bigger... yet.

I do have a drop case for it, and a screen protector (which has been broken and replaced.)

I am stunned that more of them don't offer water protection.

#### markr6

##### Flashaholic
I have 1 and 2 amp charges in the car. I'll use 2 amps for up to 70% and 1 amp beyond that.

Good thinking, but I think your phone pretty much does that anyway. I could be wrong, but even if it accepts 2amps, once it gets closer to 100% it drops off. Just a guess, but something like 800mA once it hits 85%. Same as charging an 18650 at 2amps. Even if I select 2000mA on the charger, it will only be charging at something like 500mA if it's 4.12v or so.

Regarding the battery meter, I find the iPhone EXTREMELY accurate. I'm not sure about other brands. I've tested this in real life so many times while backpacking, squeezing out every bit. Even under 10%, I can effectively manage it to last a long time. I never have any sudden drops in percentage, unless it's cold...then you're screwed!

#### StarHalo

##### Flashaholic
Regarding the battery meter, I find the iPhone EXTREMELY accurate. I'm not sure about other brands. I've tested this in real life so many times while backpacking, squeezing out every bit. Even under 10%, I can effectively manage it to last a long time. I never have any sudden drops in percentage, unless it's cold...then you're screwed!

..so long as the battery is in perfect condition - the iPhone never "recalibrates" for battery wear, so after a few months you'll notice the phone dying at ~15%, sometimes you'll plug the phone in and the meter will instantly jump ~20%, etc.

#### markr6

##### Flashaholic
..so long as the battery is in perfect condition - the iPhone never "recalibrates" for battery wear, so after a few months you'll notice the phone dying at ~15%, sometimes you'll plug the phone in and the meter will instantly jump ~20%, etc.

I've actually never seen that with my 2+ year old iphone 5, and now my 2 year old iphone 6. I've seen it when hiking in 0° weather, but that's to be expected. Otherwise, it's spot on.

#### Poppy

##### Flashaholic
I believe that there is a method to have the phone re-calibrate. I may have read about it on battery university. I guess that will work on iphones as well as others.

#### RobertMM

##### Flashlight Enthusiast

It has a battery voltage and temperature monitoring feature.
You can view battery voltage at different the percentages displayed on the phone battery meter/bar e.g. 40% battery shows 3.8V on CPU-Z.

This is how I discovered that my recent Sony phones had 4.35V packs in them, and now I only charge to 95% to prolong life.

#### reppans

##### Flashlight Enthusiast
Hi Poppy,

Here's one more data point - a military study testing how various charge cycling habits impact permanent capacity loss and it seems to dovetail nicely with the above Battery University article. After high temps, it seems to me high peak and average voltage is the next most stressful to Li-ions.

I personally use ~50% capacity per day with my iProducts and cycle on 30-80-30ish basis using a light timer set to charge ~6am so all I need to do is plug-in at night, and my device is ready when I wake up. The light timer allows the device to sit at ~30% all night for lowest average voltages, and of course keeps the max charge in the ~80% range. All I may need to do is vary the end time if I have unusually usage - only takes a few seconds, but most folks would not be willing to do so. If traveling, I usually charge in the morning while getting ready and set my iPhone's timer (~1min/1%). I also EDC a few ways to charge my phone in case of emergencies.

#### Poppy

##### Flashaholic
Hi reppans!
Thanks for the reply. I have seen you reply similarly once before, but NOW, this time, it really makes sense.

Thanks for taking the time, and sharing. :thumbsup:

Poppy

#### Capolini

##### Banned
Thanks everyone,,,,,,,,,,,,,I am going to charge mine to 90% and never let it get below 40%.:thumbsup:

#### markr6

##### Flashaholic
I have to laugh because every time I look at my wife's iPhone 6 (she just got it), it's at something ridiculous like 8%. On the other hand, mine is two years old and I've seen mine that low maybe 3 times...when I was backpacking for 3 days...with 11°F highs (tried to keep it warm but taking photos for even 10 seconds at a time in 0°F really saps the power.)

She gets mad when I "tell her how to use her phone". I stopped trying after 10 times, so I told her not to whine next year when it's not holding a charge well.