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When your laptop's battery is 100% charged, should you leave it plugged in so any battery power doesn't get used, or will that cause overcharging, overheating, etc.? Should the laptop be unplugged when the battery level is 100%?
I'm asking because my laptop's screen tends to get dim when unplugged, so I don't like to run it on battery.
Click Upvote
Posted 2009-07-25T15:01:12.930
Reputation: 4 000
182
This page has a good answer: "it depends"
The answer is: YES and NO, it depends on the situation.
Having a battery fully charged and the laptop plugged in is not harmful, because as soon as the charge level reaches 100% the battery stops receiving charging energy and this energy is bypassed directly to the power supply system of the laptop.
However there's a disadvantage in keeping the battery in its socket when the laptop is plugged in, but only if it's currently suffering from excessive heating caused by the laptop hardware.
So:
In a normal usage, if the laptop doesn't get to hot (CPU and Hard Disk around 40ºC) the battery should remain in the laptop socket;
In an intensive usage which leads to a large amount of heat produced (i.e. Games) the battery should be removed from the socket in order to prevent unwanted heating.
The heat, among the fact that it has 100% of charge, is the great enemy of the lithium battery and not the plug, as many might think so.
splattne
Posted 2009-07-25T15:01:12.930
Reputation: 14 208
13
+1, nicely explained. BatteryUniversity is one more place for good information. http://www.batteryuniversity.com/
– nik – 2009-07-25T19:41:52.11334
Removing the battery is NOT recommended for MacBooks. These actually run slower when you unplug the battery, as the A/C adaptor cannot provide all peeks that may occur in power usage. I guess this may be true for other brands as well, so even though it may increase battery life, I'd not recommend to take the battery out for any brand. See http://www.tomshardware.com/news/apple-macbook-pro-battery-benchmarks,6643.html and http://support.apple.com/kb/HT2332
– Arjan – 2009-07-26T09:10:53.197Good point, Arjan. BTW: I don't remove the battery on my Macbook Pro, because it dissipates the heat very efficiently. The bottom line is: it's a conundrum - performance against battery life. – splattne – 2009-07-26T09:30:23.727
@StefanSeidel Your reasoning is incorrect. Leaving a battery in a plugged in laptop is not storing it. It's plugging it into a smart maintainer that is specifically designed to optimize the battery's lifespan. – David Schwartz – 2016-06-20T18:05:54.230
@DavidSchwartz I was referring to 100% charge. If your laptop (and most do) charges the battery to 100%, you are effectively storing it inside a warm place (you laptop when it's operating). No battery management system will "top up" a Li-Ion battery if its voltage/charge level is high enough as it would kill them very quickly. Which means that no charge will go into the battery and no charge will go out of it except self-discharge. There is no factual difference to storing it except for the (detrimental) higher temperature. – Stefan Seidel – 2016-06-20T18:11:02.067
@StefanSeidel The battery manager can discharge it if it wants to. And it can charge it if it's not fully charged if it wants to. It is designed by experts who know the specifics of the charger, laptop, and battery chemistry. They would only hold it at 100% if that's what they thought was best or the user configured it because that's what they thought was best. It is nothing like dumb storage where no intelligent agent can do any topping off or draining. – David Schwartz – 2016-06-20T18:18:42.560
2@Arjan, does this means that the battery is still used sometimes when it's 100% charged? Then the first part of the answer isn't correct either... – Steven Roose – 2012-08-10T11:06:38.080
@splattne, is the fact that the battery get's bypassed when 100% full brand-independent? I would indeed think that that is the ideal way of behaving for a laptop, but is this implemented in all laptops? – Steven Roose – 2012-08-10T11:07:33.463
@Steven, if I understand the Apple support page correctly, then MacBooks may use some power from the battery when they are plugged in on AC power, but only at moments where the Mac needs a lot of power. I assume it doesn't matter if the battery is fully charged or not. – Arjan – 2012-08-10T13:34:29.403
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Nice, but that site doesn't tell the whole truth. You can read here that when storing Li-Ion batteries (and leaving them in the laptop is essentially storing them), their capacity will decrease unrecoverably. You will see that at 100% charge this loss of capacity is very high, whereas at 40% charge it is much lower. Thus, keeping a battery in the laptop when it's not needed is very detrimental to it's life span. Also, it increases the risk of applying "top-up" charges, which again will shorten the life span.
– Stefan Seidel – 2012-09-18T21:20:49.950It's best if the laptop charger setup had a setting where you can tell it to only charge to 60-80% of capacity. This greatly extends battery life. – Daniel R Hicks – 2012-10-04T20:08:38.107
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From a view point of your battery's health you should keep the laptop plugged into the wall and unplug the battery from the laptop. Not because of over charging or whatever, but because of the heat generated by the laptop. By removing the battery it will be cooler, which is good for the battery.
If you were to unplug the laptop from the wall, you would start to drain the battery, and would have to recharge it later. Since the limiting factor on laptop batteries (all rechargeable batteries, actually, that I know of) is the number of times they can be charged and drained, any time you can avoid draining the battery will make it last just that much longer.
Mike Cooper
Posted 2009-07-25T15:01:12.930
Reputation: 2 036
Your first 2 sentences don't make sense? – Click Upvote – 2009-07-25T16:19:23.267
Sorry, i realize now my prepositions were confusing. I edited it to be more specific. – Mike Cooper – 2009-07-25T17:28:53.540
3It never crossed my mind that you could use a laptop without the battery. Great! I have a spare laptop whose battery is almost dead. Removing would lighten the weight. – lamcro – 2009-07-25T18:58:47.133
1some laptops will not function without the battery. You will know if this is the case because the moment you try to unplug the battery the system will shut off immediately. There are only a handful of laptops that do this however. So an "expedition" is in order. – Axxmasterr – 2009-07-25T19:05:53.637
@MikeCooper It's not about how much juice the charger can supply, it's about how rapidly it can increase the amount of juice it's supplying. The cord between the power supply and the laptop has a lot of inductance.The battery is needed to hold up the input voltage when power demand spikes. – David Schwartz – 2016-06-21T07:16:52.170
More than a handfull these days. More than 50% of the laptops I come across won't boot or stay running when the battery is removed. – Polynomial – 2012-02-08T15:41:25.793
The vast majority of laptops will run slower with the battery removed. – Daniel R Hicks – 2012-10-04T20:10:39.930
Really? I have never seen this behavior. Most laptops will run slower when they are unplugged from power and running on battery, but if they have to slow down while plugged in without a battery that means that the charger is not supplying enough juice, and the battery would drain even if the charger was plugged in. In other words, citation needed. – Mike Cooper – 2012-10-11T17:29:19.453
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This all depends on the type of material the battery is made out of. Each battery material has different ideal characteristics. Look on your battery label and determine the type of battery it is. (i.e. lithium-ion (Li-ion), nickel-metal hydride (NiMH), nickel-cadmium battery (NiCd), etc. Once you determine which type of battery it is simply google the material, and read about the capabilities. This should tell you all and more of what you would like to know.
A note on charging.. Not all charging circuits are created equal, so if you have a deficient charging circuit, you might indeed want to unplug the battery after it has been fully charged like was suggested above.
Axxmasterr
Posted 2009-07-25T15:01:12.930
Reputation: 7 584
2trickle chargers or low current chargers, in particular, tend to not cut off when the battery is at 100% charge and can degrade battery capacity over time. – Jeff Leonard – 2009-07-25T22:38:55.700
True, but laptops don't use trickle chargers. They use chargers that DO cut off at 100% charge. – Jamie Hanrahan – 2015-03-19T06:25:55.257
All laptops made within the last decade use lithium-ion batteries. – intgr – 2015-04-07T07:47:48.750
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Apple has a very handy site about the batteries used in their products. While a fair chunk of it is specific to Apple products, there's a good amount of information in general about modern batteries. For example, do you know how to properly store your battery if it will be unused for some number of weeks?
The short answer to your question is "Almost certainly" keep it plugged in, but ensure there's plenty of airspace to allow proper cooling of your laptop's battery. Bedspreads and carpeting may be comfortable for you, but are far from it for your laptop's battery.
Mechcozmo
Posted 2009-07-25T15:01:12.930
Reputation: 111
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This is simple, and the best way to keep your battery life maintained. Exactly what I do:
As my laptop is a desktop replacement, because I prefer laptops, this is what I do. And it comes with an excellent result.
Be sure to let the battery get to room temperature before recharging!
11Do you have a link describing physics of your approach? – stim – 2010-04-06T13:18:20.943
1-1 What you have described is merely extending the batteries life. Which is not asked in the OP. – HaydnWVN – 2011-12-15T08:04:11.537
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I remember something from Nokia about how leaving mobile phones plugged in after they were fully charged caused an increase in overall energy usage, as compared to unplugging when charged and recharging when needed. This was part of some green initiative. I would imagine that laptops are the same. Therefore, by leaving your laptop plugged in while turned off and fully charged, you may be increasing the size of your electric bill.
pcapademic
Posted 2009-07-25T15:01:12.930
Reputation: 3 283
No. Modern power bricks dissipate very little power when inactive. – Mechanical snail – 2011-09-19T20:44:04.413
They still use more power than when they're unplugged. Also, there's no way to tell which ones are modern (just like NiMH) unless you measure. But in practice it probably is just green lip service. – XTL – 2012-03-07T12:52:43.467
28You can increase the brightness of the screen when it's running on battery. Differs machine to machine, but most laptops have function keys for screen-brightness – dbr – 2009-07-25T15:23:37.323
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See also yesterday's "Is it better to use laptop on battery or on AC power?" at http://superuser.com/questions/12358/is-it-better-to-use-laptop-on-battery-or-on-ac-power/
– Arjan – 2009-07-26T09:08:14.1071By the way, this question is many years old and the answers are largely obsolete as well. The answer today is that you should leave it plugged in. There is no advantage to unplugging it -- there is nothing it can do while unplugged that it can't do when plugged in. But there are huge advantages to keeping it plugged in -- there are things it can do when plugged in that it can't do when unplugged. The laptop's battery controller is smart enough to do what's best -- the guys who designed it know your battery system in great detail. – David Schwartz – 2016-11-29T03:03:48.583
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Possible duplicate: http://superuser.com/questions/12358/is-it-better-to-use-laptop-on-battery-or-on-ac-power (probably won't get closed though)
– Hello71 – 2010-08-02T00:43:22.5431Can I just say fantastic question, I've always wondered myself but never asked before. – Robert Massaioli – 2011-01-20T01:33:04.327
1If the battery life is not a concern, which way saves electricity? – None – 2011-11-18T04:57:39.963
Keeping a standard Li-Ion battery charged at 100% shortens its life. Charging to 60-80% is better, in terms of battery life. Some laptops allow the charge % to be adjusted for this reason. – Daniel R Hicks – 2012-01-05T01:17:37.537
1If you have a Thinkpad (and probably for other machines also), there is a setting in the Bios for screen dimming on battery. This can be reached when you power the laptop on (on a Thinkpad you press the ThinkVantage button, on another machine it will probably be a Function key). – Joel in Gö – 2010-01-18T09:11:15.287