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Correct way to charge rechargeable devices (iPhone, laptop, toothbrush)?
December 30, 2013 7:35 AM   Subscribe

I've just been told at the Apple store that it's a bad idea to keep the iPhone plugged into the power for long periods when fully charged, and that if possible I should really only charge it when it tells me to (ie. when the battery is almost dead).

My 2-year old iPhone loses a charge very quickly, so I have it recharging whenever I'm near an outlet. I'll be getting a new iPhone shortly and would like to know what the optimal charging schedule should be. I'm also wondering if other rechargeable devices that are ordinarily constantly plugged into the power, like my electric toothbrush in the bathroom, or my laptop in my home office, should always be disconnected until the battery dies.

Or is it fine for the battery to be run dry only once in a while, and otherwise constantly charging? And if so, what is once in a while, and does the rule apply to all rechargeable batteries?
posted by Dragonness to Technology (7 answers total) 22 users marked this as a favorite
 
I've also been told that this is a best practice, but find that if my iPhone 4 is having trouble holding a charge, it usually has to do with apps running in the background that need to be closed. Some of them seem to suck battery way more than others. As long as I manage that okay, "put it on the charger every night" has done me just fine.
posted by Sequence at 7:38 AM on December 30, 2013


Here is a full explanation of what to do and why you hear conflicting advise.
posted by Houstonian at 7:40 AM on December 30, 2013 [7 favorites]


This is great, thanks so much both of you. Pretty much every app I've ever used was running in the background! I've also turned off the background refresh on almost everything.
posted by Dragonness at 8:30 AM on December 30, 2013


Though it is an extremely common misconception (sometimes even parroted by Apple Store employees) you do not need to close background apps. With rare exceptions (music, GPS), those apps are not "running" in any sense, and are only displayed in the switcher as a convenient "recently run" list, more akin to your browser history.

The advice in the Lifehacker article is sensible, as is this resource from the horse's mouth.
posted by Mr. Anthropomorphism at 9:05 AM on December 30, 2013 [1 favorite]


As of iOS 7, background apps can take a non-trivial amount of battery (via "Background App Refresh").

In short, prior to iOS 6, there was effectively no background processing (almost all apps stayed suspended in the backgroun). In iOS 6, some apps were allowed to run in the background (for instance, music apps). In iOS 7, all apps can run in the background via Background App Refresh, but that ability can be turned off on a per-app basis.
posted by saeculorum at 9:13 AM on December 30, 2013 [1 favorite]


Apple has allowed limited background processing by 3rd-party apps since iOS 4. iOS 7 did broaden background processing support and provide user controls, and it's worth checking the settings there. The truth is though that most apps "running" in the background as revealed by the iOS app history, really aren't.

That Lifehacker article on battery care seems to create as much confusion as it clears up.

Yes, the lithium polymer batteries used in most mobile phones, tablets, and laptops for the past 5+ years don't have the memory effect older NiCad and NiMh batteries. Yes, they also hate being fully discharged, or overcharged, or charged too quickly, but that is why the devices, and even the batter packs themselves, have dedicated battery management circuitry. That circuitry doesn't just keep track of how much charge is left, it uses that information to optimize charging.

One result is that while it is indeed terrible to run a Li battery down, or to overcharge it, it is pretty much impossible to do in normal use because the battery management circuit cuts things off while there is still a safe reserve charge left, and cuts charging off before things go too far. There is some risk of excessive discharge if the device isn't charged in a timely manner after hitting its discharge cutoff, but timely isn't hours, or even days, its weeks. When your phone shows 100% charge, that is 100% of a safe charge, and when it turns off because the battery is run down, there is still a safe charge remaining.

In the end though, rechargeable batteries in mobile devices are treated as limited-life parts. Even a brand new, properly charged Li-poly battery will loose maximum capacity over time, and on top of that, they loose a little capacity with every charge-discharge cycle. In addition, there is some variation in quality. Some start life weaker than others, and age faster. Battery management circuitry can screw up too. If your battery life is noticeably significantly degraded after a year or two, and it isn't because of software, then you had bad luck and you should consider replacing the battery. Apple should do it for free under warranty/AppleCare, and may still do it free out of warranty.

As to what you should do with your new phone: Use it. Charge it when convenient or necessary. Don't worry if you charge it to "100%," because the battery management is keeping you from overcharging. Don't worry about only charging it up part way when you are in a hurry, because charging and discharging 20% only causes about 20% of the wear and tear as a "full" cycle. Avoid letting your phone drop into the red not because its bad for the phone, but because your phone isn't any good to you if the battery runs out. It isn't a bad idea to let it run down until it turns off, or close to it, every once an a while though, because, as noted, it helps the circuitry recalibrate, and also, LiPOLY BATTERY STUFF.

This same advice holds for laptops, with the caveat that it is worth being more deliberate about doing a full charge/discharge cycle if you tend to plug your laptop in when you use it.

These days, particularly with Apple products, the user shouldn't have to worry about babying the battery, beyond avoiding use in high temps (>95F), that is the software/hardware's job. Any added improvement you can get by changing your behavior is probably minor, and isn't going to come from following ill-informed advice (including, unfortunately, advice from Apple retail employees)
posted by Good Brain at 12:22 PM on December 30, 2013 [2 favorites]


In all but the stupidest or cheapest of devices, the battery's charging circuits will take care of the battery in the proper manner. A lot of the advice about not fully charging and discharging is correct about the individual cells, but the circuitry masks all of that. Your battery meter might go from 0% - 100%, but the internal cells are most likely being kept in their target range, whatever that is. (Like 40% to 90%, for example)

By far, the biggest thing that kills lithium ion batteries is time. (assuming you don't abuse them) The instant the cells are manufactured, they start to decay and lose lifespan.

To second Good Brain's advice: don't worry about optimizing your battery life. It takes a lot of hassle and is worth practically nothing. As long as you don't abuse the battery, you are fine. Don't let it discharge all the way, and *really* don't let it sit around once it gets discharged.
posted by gjc at 4:36 AM on December 31, 2013


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