

It's not bad to leave your laptop plugged in - garret
http://www.marco.org/195827279

======
KirinDave
There is one point that should be noted for macbook pros (and probably many
other varieties of laptop).

> When plugged in, the battery is not in use. The laptop’s power circuitry
> bypasses the battery unless it’s needed. Depending on how smart the charger
> is, it may occasionally poll and “top off” the battery if its charge
> decreases to a certain threshold below 100%, but this is rarely needed in
> practice.

Not strictly true.

If you plug in your macbook, your battery is still being used. Evidently the
power supply actually cannot meet the peak power demand of the system, so the
battery needs to be there to provide for that [1] [2]. Apple also feels that
the conditioning the battery receives while it interacts with a powered system
increases its longevity.

Generally the power adapter provides more power than your machine is using, so
obviously it can charge. But if you remove your battery and benchmark your
system, you'll find that your system is limiting itself back about 20-30% to
account for the lack of battery.

References: [1] <http://support.apple.com/kb/HT2332> [2]
[http://www.tomshardware.com/news/apple-macbook-pro-
battery-b...](http://www.tomshardware.com/news/apple-macbook-pro-battery-
benchmarks,6643.html)

~~~
bonsaitree
Correct.

In "modern" laptops with Li or Li-Poly batteries, it's really more about the
embedded intelligence, or lack there of, of the power regulator relative to
the reactance headroom of the power source (relative to system demands) than
the battery itself.

Some systems, notably netbooks, have virtually zero variance in their reactive
power loads so the manufacturer can skimp a little on the regulator--not so
for full-featured notebooks with multiple drive and fan servos powered by
induction motors. A MackbookPro running only an SSD and idling fans has the
same effective reactance profile of a netbook.

A suitable analogy can be made with automobile transmissions. Two identical
models can have vastly different mpg performance and component wear with
different transmissions under different loads though they weigh nearly the
same, run on the same fuel, and have the same horsepower/torque curve.

------
arfrank
> When Apple decides whether a battery is defective or has been worn out
> normally, the “special utility” they run is System Profiler. You can run it,
> too. Check the Power section, and it’ll tell you your battery’s cycle count,
> the intended capacity at manufacture, and how much capacity per cycle
> remains. Apple technicians compare the cycle count to the capacity loss. If
> your battery has lost a lot of capacity in its first year but hasn’t
> performed enough cycles to reasonably correlate to the capacity loss,
> they’ll replace it under warranty.

Apple actually does have a special application that they run to determine if
the battery should be replaced and if its under warranty or not for that
replacement. I recently got a new battery from them and the genius pulled out
an iPod Mini and booted from it and ran what looked like a Carbon app, it was
certainly unpolished and reminded me of the OS 9 days. It pulled data from
what I assume was the battery and plot it on a 2-D axis, where depending on
what quadrant it was in they make a determination on replacement and warranty.
That all being said, it might just be an easy way for them to make a
determination instead of going to system profiler, but it'd make the most
sense to have a standard tool for the entire company.

~~~
__david__
More than just looking like an OS 9 app, they boot your computer directly into
the app (off a USB stick in my case). Supposedly their hardware diagnostic
tools also have the same look and feel. It's probably so they can code
directly to the hardware without a messy OS in the way.

I tried to ask the guy about the graph and what the quadrants meant but he
claimed it was secret and wouldn't tell me what the axes represented (they
were unlabeled).

There was also a whole lot of numbers on the right hand side and he looked for
a number in there but, again, wouldn't tell me which ones were important to
their warranty program.

------
JeremyChase
This article focuses entirely on cycling as a rational for leaving the laptop
plugged in, but heat and charge state are staggeringly more important to
absolute capacity.

A fully charged lithium battery loses absolutely capacity much more quickly
than a partially charged battery. Even worse, a warm, fully charged battery
will lose absolute capacity at an astounding rate. A battery at 140F will be
down to 60% of its initial capacity after 3 months if it is fully charged
during that time. _[1]_ If the battery could be maintained at 40% charge
during that time it would still have 85% of its capacity after a full year of
use, even at the same temperature.

This means that leaving a laptop plugged in will kill the battery in a very
short time. The alternative is to let the battery continually cycle down and
then charge it again. This isn't a good solution either because the extra heat
very well may offset any benefit of keeping the battery at a lower charged
state.

All in all, I think it means that a laptop is not meant to be on all the time;
unless you are willing to replace the battery at fairly regular intervals.

 _[1]_ <http://www.batteryuniversity.com/parttwo-34.htm>

------
cubicle67
I have a 1st gen unibody MacBook, about 15 months old. It's spent almost its
entire life plugged in, but with occasional excursions away from power for the
day.

These are the figures iStat gives me for the battery at the moment: 100%
Health and 133 cycles. It still gives me 5+ hours battery life, enough to mean
I don't usually take the power cord with me.

------
Tichy
Really, the manufacturer should manage the battery for me when the notebook is
connected to a power outlet. I don't want to have to worry about that kind of
thing. Like, if it should run on battery once per month, just make it do so
automatically. Is that too much to ask? Maybe some physical law prevents that
kind of thing?

~~~
grogers
Not exactly a law, but:
<http://en.wikipedia.org/wiki/Principle_of_least_astonishment>

If your laptop battery suddenly started dropping towards zero charge when it
was plugged in, you wouldn't be at all concerned? What if you needed it at
full charge to take it somewhere?

~~~
Tichy
Then at least the OS should give me a little reminder icon, "you haven't
discharged your battery in n weeks". I see what you mean, but it seems
unlikely that is the reason?

------
coryrc
He's wrong on the "leave your laptop plugged in always" point, but presents a
bit of a false dichotomy.

Your battery will last longer than three years if you keep it below 80% State
of Charge. A battery below 80% has nearly no loss of capacity over time. If
you have a good laptop with a removable battery, taking it out once it reaches
80% will extend its life by years.

<http://www.slate.com/id/2234009/>

<http://www.batteryuniversity.com/print-partone-19.htm>

------
jaxn
I just assume I need to buy a new battery once a year. The life of the battery
seems to decrease over time and budgeting for a new battery each year seems to
work for me.

I usually keep a laptop as my primary for 2 years, so it is only one
additional batter per machine.

------
icco
iFixit wrote a great article behind maintaining your battery back in November,
covers a lot of similar data as the two battling arguments on HN today.

<http://www.ifixit.com/blog/?p=1897>

------
Estragon
The folks at the Verizon store the other day were telling me that it's best to
let a phone battery run to near-depletion before replenishing, because they
only have a finite number of depletion-replenishment cycles, and running the
battery to, say 50% capacity then replenishing uses up one of these cycles.

I have no idea whether or not this is true.

~~~
pronoiac
For Li-Ion batteries, which I think are the norm, they're wrong, & that course
is about the worst for your battery life. Deep discharging once a month or so
can be helpful, but, say, every day or two, is not. Charging halfway counts as
half a charge, so lots of small charges is much gentler than many big charges.

See <http://www.batteryuniversity.com/partone-14A.htm>

~~~
Estragon
Thanks for the information.

------
RevRal
Well, I've _tried_ to worry about this stuff, but it's too much of a hassle.
Instead, I replace the cells in my battery:
<http://www.youtube.com/watch?v=BtqRvAu71Gw>

Works for my laptop battery and is super cheap, though caution please.

------
eoinof
From the apple website article linked in the posting: "Apple does not
recommend leaving your portable plugged in all the time. An ideal use would be
a commuter who uses her MacBook Pro on the train, then plugs it in at the
office to charge. This keeps the battery juices flowing."

------
noonespecial
I don't know if its still true or not, but the chemistry in a lithium battery
breaks down over time, reducing its capacity to store charge (even when not in
use). This is greatly accelerated by both heat and charge state of the
battery.

The best bet for long term storage was "40/40". Discharge the battery to 40%
and store it at 40 degs F. You could go as high as 60 before getting into the
steep part of the deterioration curve.

The bottom of a running laptop seems the exact opposite of this ideal
environment. Your laptop is going to hold it at 100% charge and heat it to
90-100 degs. If you're going to leave your laptop plugged in for a long time,
it might be best to remove the battery and place it on a shelf nearby.

------
Willie_Dynamite
Somehow, When it comes to this subject I tend to trust someone working on
battery technology at Lawrence Berkeley more than I do a webapp developer.

~~~
SpacemanSpiff
I thought the same thing but then I read the marco.org article and realized
that it wasn't a response to the This Week in Batteries blog, but to an
unrelated article that seems to recommend full cycling the battery. I believe
what was meant by the marco.org article is that regular _full cycling_ is a
lot worse for your battery than simply leaving it plugged in.

The This Week in Batteries blog recommends extending the life of your battery
by not constantly leaving it topped off at 4.x volts per cell (which causes
the internal aging process to accelerate)

So in essence, they're probably both right. When people ask me what's best for
their laptop battery I say charge it to 65% and put it in the refrigerator.
Not so great for using your laptop however.

------
lutorm
That's what I thought: Deep-cycling Li-ion is much worse than keeping them
charged up.

------
mtarnovan
I beg to differ. I used my last laptop 10+hours/day always plugged and the
battery wore off after 6 month. My current laptop, exactly the same. I only
used it plugged in and now, after 10 month, the battery lasts 5 minutes.

~~~
ugh
Probably a coincidence. Never trust anecdotes when it comes to computer
problem stories.

(Also: never read in support forums before deciding what to buy. What you are
seeing is most likely not the average case.)

------
dfox
while it is ertainly not good idea to intentionaly deep-cycle Lithium based
batteried, there is also another good advice: remove battery when you intend
to use laptop for long time (more than sy 3 hours) on mains power. Althought
lithium-based batteries tend to lose capacity with age, this effect is
strongly correlated with temperature and running laptop produces heat that
will increase battery's temperature. (this requires wall suply that is able to
cover laptop's peak power usage, which is nowadays not always the case)

------
zokier
AFAIK if you don't need the battery, it would be best to store it in a cool
place, fully charged. Li-ion batteries don't like heat, and the bottom of a
laptop is a quite warm place.

------
hockeybias
Thanks for this!

