Ask HN: Should I unplug my laptop charger at 100%? • Hacker News Board

Re: Ask HN: Should I unplug my laptop charger at 100%?

#171

Post by Lawtonfogle » Mon, May 04, 2015, 8:51 PM UTC

gr8b8m8-88 wrote: post #104

toxicFork wrote: post #13

Earlier quoted context omitted.

This is my favorite technology superstition, some citation would help many people sleep easier it seems.

Statistics and citations today is the Bible quotes / racial stereotypes of yesteryear. Some modern-day pseudo-scientist poster will cite some study that says "80% of chargers waste power if left plugged in at 100% charge" will then draw the logically faulty conclusion that therefore you should unplug your charger. The fact that the statistic study necessary had to ignore extra variables like if you have a lot of stuf…

We can try to arrive at an exact answer.

First, we need to start by assuming a sphererical laptop...

Re: Ask HN: Should I unplug my laptop charger at 100%?

#172

Post by myth_buster » Mon, May 04, 2015, 8:51 PM UTC

DavideNL wrote: post #107

bkanber wrote: post #58

Source: I have a master's degree in mechanical engineering in hybrid vehicle powertrains, and a big part of my research was battery technology. I spent some time working with the folks at National Semiconductor learning this, so I have several primary sources. Disclaimer: my knowledge of the field is from ca 2010. 1) Lots of deep discharge cycles do negatively affect battery life. Try not to jump between 0% and 100%…

That's nice to know. However, i'd rather buy a new battery after 5 years (if my laptop is still fit and the battery is dead), than having to complicate my life and think about when to unplug or charge my laptop multiple times each day for 5 years... My Macbook air from mid 2011 is currently at 100/6700*5629 = 84% battery health. (6700 = design capacity, gathered from "ioreg -l -n AppleSmartBattery -r".

Could you elaborate on how you arrived at the "5 years" lifespan for batteries having charge state of 0-100%?

Re: Ask HN: Should I unplug my laptop charger at 100%?

#173

Post by jffry » Mon, May 04, 2015, 8:52 PM UTC

johnymontana wrote: post #167

DavideNL wrote: post #107

Earlier quoted context omitted.

That's nice to know. However, i'd rather buy a new battery after 5 years (if my laptop is still fit and the battery is dead), than having to complicate my life and think about when to unplug or charge my laptop multiple times each day for 5 years... My Macbook air from mid 2011 is currently at 100/6700*5629 = 84% battery health. (6700 = design capacity, gathered from "ioreg -l -n AppleSmartBattery -r".

Could you clarify how you arrived at 84% battery health? After the command "ioreg -l -n AppleSmartBattery -r" I see DesignCapacity, but where does the other number (5629) come from? I'd like to compute battery health myself...

running

  ioreg -l -n AppleSmartBattery -r | grep -i capacity

gives me

  "MaxCapacity" = 8329
  "CurrentCapacity" = 8002
  "DesignCapacity" = 8440

I'm guessing MaxCapacity or CurrentCapacity (I'm at 100% charged on a ~1 year old MBP, so I don't know which number is appropriate)

Re: Ask HN: Should I unplug my laptop charger at 100%?

#174

Post by bkanber » Mon, May 04, 2015, 8:54 PM UTC

jules wrote: post #153

bkanber wrote: post #58

Source: I have a master's degree in mechanical engineering in hybrid vehicle powertrains, and a big part of my research was battery technology. I spent some time working with the folks at National Semiconductor learning this, so I have several primary sources. Disclaimer: my knowledge of the field is from ca 2010. 1) Lots of deep discharge cycles do negatively affect battery life. Try not to jump between 0% and 100%…

What if you're mostly using the laptop near a power outlet? Wouldn't it be better to keep it plugged in to avoid charging/discharging the battery at all?

No. Leaving a battery at 100% is bad for the battery's life. Just as bad as deep cycling all the time. Even if your laptop is stationary, knock the charger out once a day and let it run on battery power for a bit.

Re: Ask HN: Should I unplug my laptop charger at 100%?

#175

Post by m3Lith » Mon, May 04, 2015, 8:54 PM UTC

BorisMelnik wrote: post #123

sigmar wrote: post #114

Earlier quoted context omitted.

>plug in and let charge to 90%, unplug and use for a couple of hours, plug back in at 50% or so, rinse and repeat. My thinkpad has a mode for keeping a healthy battery that stops charging at 90%, then trickle charges to keep it there (it also allows for fine tuning of this behavior)

excellent - what software does this? Built into the OS or a separate application?

It's definitely a separate app. Lenovo has various versions of "Power/Energy management" apps available depending on the specific model of the laptop. Not sure about other manufacturers though.

Re: Ask HN: Should I unplug my laptop charger at 100%?

#176

Post by t0mbstone » Mon, May 04, 2015, 8:56 PM UTC

If unplugging your charger at 100% and letting your battery run to 84% or whatever, and then plugging it back is so good for it, why doesn't Apple (or any other laptop manufacturer) just have the power controller do that automatically when your laptop is plugged in?

I call malarkey on all of it. I've had my laptop plugged in for years and it sits at 100% most of the time. I don't have time to deal with that kind of hassle, even if it is true.

Re: Ask HN: Should I unplug my laptop charger at 100%?

#177

Post by geoelectric » Mon, May 04, 2015, 9:05 PM UTC

mc32 wrote: post #168

bkanber wrote: post #58

Source: I have a master's degree in mechanical engineering in hybrid vehicle powertrains, and a big part of my research was battery technology. I spent some time working with the folks at National Semiconductor learning this, so I have several primary sources. Disclaimer: my knowledge of the field is from ca 2010. 1) Lots of deep discharge cycles do negatively affect battery life. Try not to jump between 0% and 100%…

It'd be nice if the battery controller/charger had the intelligence to make these optimizations transparent to the end user. So present them with 100% or whatever, but in actuality, the battery is at 90%, most of the time it's plugged in, and so on.

I thought this was actually standard operating procedure for laptop batteries (or really, anything using lithium batteries). Similarly, 0% is actually more like 5 or 10%.

If you actually deep discharge a lithium battery to 0%, think they'll sometimes have problems taking a charge again. You see this occasionally when someone has taken to 0% on the meter, then let it self-discharge on the desk for a long time.

Re: Ask HN: Should I unplug my laptop charger at 100%?

#178

Post by dfox » Mon, May 04, 2015, 9:08 PM UTC

BorisMelnik wrote: post #123

sigmar wrote: post #114

Earlier quoted context omitted.

>plug in and let charge to 90%, unplug and use for a couple of hours, plug back in at 50% or so, rinse and repeat. My thinkpad has a mode for keeping a healthy battery that stops charging at 90%, then trickle charges to keep it there (it also allows for fine tuning of this behavior)

excellent - what software does this? Built into the OS or a separate application?

On ThinkPads this can be (or maybe used to be) configured in one of the preinstalled ThinkVantage utilities (Power Manager). But I believe that the whole charging logic itself is really in EC firmware and this application is only user interface for that.

As an aside: the mechanism works in slightly different way (at least on all of my 4 thinkpads of different generations). There are two thresholds, maximum battery capacity when charging can start and capacity when charging stops, the aforementioned application even seems to have some kind of logic to set these thresholds according to battery aging.

Also, trying to keep Li-ion cells charged to constant state of charge is not good for their lifespan. What is commonly known as trickle-charging (charging by infrequent, short but large pulses of current) is actively discouraged by most cell manufacturers, sometimes even citing safety reasons.

Re: Ask HN: Should I unplug my laptop charger at 100%?

#179

Post by a3n » Mon, May 04, 2015, 9:08 PM UTC

bkanber wrote: post #58

Source: I have a master's degree in mechanical engineering in hybrid vehicle powertrains, and a big part of my research was battery technology. I spent some time working with the folks at National Semiconductor learning this, so I have several primary sources. Disclaimer: my knowledge of the field is from ca 2010. 1) Lots of deep discharge cycles do negatively affect battery life. Try not to jump between 0% and 100%…

If I was going to do this, it would be at the laptop end, because that's were I'm sitting.

How long until the power plug, or the receptacle in the laptop, wears out?

How expensive is labor to fix the receptacle, compared to the cost and convenience of replacing a battery?

Unless the OS manages this for me (and maybe it does behind my back?), I'm not going to bother. But many thanks for the interesting writeup.

Re: Ask HN: Should I unplug my laptop charger at 100%?

#180

Post by skizm » Mon, May 04, 2015, 9:08 PM UTC

auganov wrote: post #48

Maybe I have bad luck, but I came to accept that every laptop battery eventually becomes a UPS for getting from the desk to bed :-)

Apple ones also?

This has happened to several dell and hp laptops I've owned or used long term, but both apple ones still keep charges for close to 3 hours even around 3 years after purchase without replacing the battery.