Charging Device Overnight

[Max Cow Disease]

I've read various tales about this on the web but I've never really found out for sure; is it possible to charge devices like tablets or phones for "too long"? I've always been fairly OCD about disconnecting my Nexus 7/iPhone when it reaches a full charge because I've heard rumours that it can damage the battery otherwise. However, I inevitably forget from time to time, and last night the Nexus was plugged in all night after being fully charged.

I'd assume that the more modern devices include some sort of disconnect circuit once the device is charged, but what are CP's surely insightful thoughts on this matter?

[sclitheroe]

There is tons of information to share and lots of myths to dispel around lithium ion battery care, but we'll start with the overnight questions.

The answer is no, you cannot harm a device by leaving it plugged in overnight. Lithium Ion battery charging follows a very strict profile, and the final phase of the process is to cease all charging - there is no trickle charge or anything going on once the battery hits 100% charge, because lithium ion batteries have no tolerance for being even slightly over-charged.

[FlameOn]

Most cell phones and other portable devices use Lithium Ion batteries now that really should not get damaged or have "memory issues" with constant recharge and discharges near full. So no, likely there won't be a problem unless you are using an older device that still uses Ni-Mh or something similar to that.

That being said, modern digital charging circuits such as the one on your Nexus have to be calibrated so it knows when a battery is full and when it is empty to prevent overcharging on a battery, constant charge/recharge when the battery is full and so your device will correctly know when the battery is "full". You might want to charge the device up to full and let it discharge all the way every once in a while so the device calibrates for the battery properly.

[sclitheroe]

Second post - let's talk about discharge. Lithium ion batteries do not tolerate deep discharges well. Although it's possible to run a battery down to 0% on the meter, what is really happening at this stage is the device is shutting down above the terminal (lowest) voltage of the battery in order to save it - if lithium ion cells fall below a certain voltage, they can be irreparably damaged and won't be capable of accepting a re-charge.

The best thing to do, on the low end of the charge spectrum, is to avoid discharging below 30% whenever possible. The bottom 30% of the charge profile is taxing on the batteries from a electro-chemical/physical perspective, and using them in that range causes more wear on the batteries.

[sclitheroe]

Third post - let's talk about charging and charging frequency

It's important to note that lithium ion cells do not suffer from "memory", which is a loss of capacity from partial charging.

A couple small charges throughout the day, to keep the battery above that 30% threshold is better, overall, for a lithium ion battery, then letting it go below 30% and receiving one big charge at the end of the day.

Another interesting facet of lithium ion battery technology is just as the bottom of the charge profile is hardest on the cells (eg. discharging them down to the very bottom of their capacity), charging to 100% is actually stressful for the cells as well - putting that last 10% of charge into a device is the roughest phase of the charge on the cells. So you're actually best off to always have the device above 30%, but below 100%.

In practical terms, this is hard to do and requires too much monitoring - so the best compromise is to aim for a 100% charge once a day at most - this is the overnight charge originally asked about. You don't want to keep stuffing the battery with that last 10% charge over and over throughout the day, because that's where a lot of the harm and degradation of the battery occurs.

Batteries should be charged when the phone is at room temperature - charging below room temperature doesn't damage the battery (to my knowledge), but charging at an elevated temperature (eg. after an epic gaming session) is an extremely good way to damage the battery. A few full recharges at an internal battery temperature of 40 Celsius is a good way to permanently knock 10-20% capacity off the battery.

[sclitheroe]

Fourth post - Calibration.

The capacity shown on your devices is an estimate of available capacity, not the gospel truth. The charging circuitry knows what a full charge voltage is, and what a terminal voltage is, as well as the approximate voltage discharge curve of a lithium ion battery. It also knows how much current it put into the device and how much current has been taken out of the cells.

We've already said that its harmful to discharge a lithium ion battery all the way to zero, but sometimes you will want to. If you notice that the indicated battery capacity is grossly wrong, you'll want to run the device until it shuts down, and then allow it to fully recharge in one go. This will allow the monitoring hardware to reset it's knowledge about how much charge can be stuffed into the battery at its current health state.

Don't do this weekly. Don't do this monthly. Do this if you feel there are significant misrepresentations about battery capacity. Every time you do this, you are inflicting a fair degree of wear on the battery.

[Max Cow Disease]

Some interesting details there that I was unaware of, thanks!

[Max Cow Disease]

Originally Posted by sclitheroe

Fourth post - Calibration.

The capacity shown on your devices is an estimate of available capacity, not the gospel truth. The charging circuitry knows what a full charge voltage is, and what a terminal voltage is, as well as the approximate voltage discharge curve of a lithium ion battery. It also knows how much current it put into the device and how much current has been taken out of the cells.

We've already said that its harmful to discharge a lithium ion battery all the way to zero, but sometimes you will want to. If you notice that the indicated battery capacity is grossly wrong, you'll want to run the device until it shuts down, and then allow it to fully recharge in one go. This will allow the monitoring hardware to reset it's knowledge about how much charge can be stuffed into the battery at its current health state.

Don't do this weekly. Don't do this monthly. Do this if you feel there are significant misrepresentations about battery capacity. Every time you do this, you are inflicting a fair degree of wear on the battery.

How do the various battery apps work, as far as battery details are concerned? Most of them seem to claim an accurate representation of battery charge (to a singular percentage point), temperature, remaining charge time, etc. Some of them also claim to alter the charge cycle so as to maximize battery life/efficiency, of which I'm skeptical.

[sclitheroe]

Fifth post - Battery service life

Lithium Ion batteries are rated for a finite number of cycles. A cycle is defined as taking the rated amount of power out of the battery, and putting 100% of that power back in (so a full discharge to a full recharge). What most people don't understand is that this is a cumulative number. If you drain 20% of the battery down, and recharge it, you've just completed 20% of a cycle. If you subsequently take 40% out, and put 40% back in, you're now up to 60% of a cycle. Take another 40% out, and put 40% back in (so your third charge of the day), and you've finally hit 1 cycle.

This supports and reinforces the notion that many smaller recharges are better overall than a deep discharge followed by a full recharge - you aren't burning up charge cycles and shortening the life of the battery by plugging it in frequently for small top-ups (unless you are doing a top-up from in the 90-100% range over and over)

Lithium ion batteries also have a finite shelf life Lithium is a highly reactive chemical, and the high power density of lithium ion cells means they are under a lot of electrochemical stress. This means that lithium ion batteries are degrading the minute they leave the factory. No matter how much you baby your cells, once you start to get up to the 3 year mark, you've permanently lost capacity due to old age. Some cells last longer, some last shorter, but fundamentally, you are fighting a losing battle against time.

[sclitheroe]

Originally Posted by Max Cow Disease

How do the various battery apps work, as far as battery details are concerned? Most of them seem to claim an accurate representation of battery charge (to a singular percentage point), temperature, remaining charge time, etc. Some of them also claim to alter the charge cycle so as to maximize battery life/efficiency, of which I'm skeptical.

They are reading the values exposed by the charging circuitry, so they are showing you the same information that the OS has access to, but maybe doesn't show you (my macbook, for example, knows all kinds of things about the battery that it doesn't tell me by default, like temp, power going out, power going in, mAH capacity, etc.)

I am highly skeptical that any of the kinds of apps you are talking about do anything to alter the charge cycle - lithium ion charging is a hybrid combination of constant current and constant voltage charging, and it is notoriously unforgiving - you really only have one technique to do it right, without risking damage to the batteries, swelling, fires, etc. It's highly unlikely that any consumer devices have a programmable charger built in - it's almost certainly a dedicated chip with a dedicated charge algorithm.

[sclitheroe]

Sixth post - leaving your laptop plugged in all the time

This doesn't apply much to mobile devices, but we should address the effect of leaving your laptop plugged in all the time.

Just as charging to 100% capacity is stressful on a battery, so is sitting at 100% charge all the time. It's literally stressful to the battery's construction - you've got a huge reserve of electrons being held in electrochemical stasis, and they want to flow and move and balance out the charge in the battery. Leaving a battery in this state of imbalance (100% charge) full time will begin to wear down the battery's ability to hold a charge.

But a lot of laptop users are plugged in a lot of the time. So what to do? My suggestion, if you put less than one cycle a week on your battery presently (see how to calculate a charge cycle above) is to artificially perform one once a week. Every Friday, unplugging until you hit 30% and then recharging will go a long way to keeping the battery healthy over its normal 3 year lifespan.

[Inglewood Jack]

God these things are finicky. Are we talking about battery or girlfriend maintenance here?

[sclitheroe]

Originally Posted by Inglewood Jack

God these things are finicky. Are we talking about battery or girlfriend maintenance here?

Well, having posted all of that information, I'd say the main thing is to just enjoy using your device.

If you follow these three rules you'll be OK:
- avoid draining to zero or very low charge levels as often as possible
- don't recharge while hot
- don't leave in hot places (in a car is the worst)

Realistically, if you don't hammer the battery with deep discharges, and don't let it cook to death in a car in the summer, the battery will probably perform well for the lifespan of the device (which is, coincidentally, about the service life of a Lion battery, 3-4 years)

[Raekwon]

Its not about being right, its how you present the info. I believe it because he sounds like he is right, lol.

[sclitheroe]

Originally Posted by Raekwon

Its not about being right, its how you present the info. I believe it because he sounds like he is right, lol.

The cornerstone of any good cult.

[Rhettzky]

Are there any issues with using your device while it's charging?

And thanks. Those are some great tips.

[sclitheroe]

Originally Posted by Rhettzky

Are there any issues with using your device while it's charging?

No. It might charge more slowly, since some of the power the AC adapter normally uses for charge goes to powering the device. But otherwise that's a normal usage pattern.

In fact, some devices (such as the Macbook Pro) will actually use the battery to supplement the AC adapter during times of peak power consumption - if you remove the battery on a Macbook Pro, it'll run slower because it knows it might not have enough juice on AC alone to handle peak loads.

[sclitheroe]

Tables 2 and 4 here show the experimental effects of deep discharge (depth of discharge), as well as extended running at full charge (or full voltage, 4.2V), on lithium ion batteries:

http://batteryuniversity.com/learn/a...ased_batteries

[psyang]

Will add that if your laptop has a "battery saver" function which ensures the battery is only charged to a certain level, use it if you are plugged in often.

My 3 year old laptop has this - the default setting is to charge the battery only to 80%. I set it to 50%. After 3 years, the battery has 0% wear. My laptop is plugged in 90% of the time. The only downside is remembering to change it to a full charge if you know you are going to be unplugged for an extended period of time.

[Bobblehead]

Originally Posted by fotze

One final question, is sclitheroe right?

Yes.