A friend complained to me that after only two years, she had to replace her laptop’s battery because it wouldn’t hold a charge. I found myself telling her that she shouldn’t keep her notebook computer plugged in continuously, because it would kill the battery faster. Then I stopped myself: Was this just outdated geek lore rendered obsolete by modern batteries?
Yes and no. It depends, of course, on what kind of battery you have. Battery technology has come a long way over the years, and surely in 2009 you don’t have to worry about how long your laptop’s been plugged in. However, one major notebook manufacturer (which ships Lithium-ion batteries) thinks you should, and suggests adding a reminder to your calendar to deplete and recharge your battery once a month. To quote: “Apple does not recommend leaving your portable plugged in all the time.”
My friend, however, has a two-year-old Dell. Cursory Googling for her model didn’t turn up the equivalent of Apple’s definitive statement, only lots of opinions which ranged from “it’s a non-issue” to “yes, it kills batteries!” Dell.com’s battery recommendations page doesn’t say anything about not keeping your notebook plugged in. HP’s battery tips page doesn’t answer the question, either. I pored through my wife’s ASUS Eee PC user guide and didn’t find any warning about continuous charging. A non-mention might make you think it’s a non-problem, but if this is an issue for Apple notebook batteries, it is for PC notebooks with lithium-based batteries too. When I asked, my Twitter followers returned mixed replies, but many notebook users (both Mac and PC) DID report anecdotal battery problems when the machine was plugged in constantly.
Other folks more educated about the differences in battery types than I am dropped knowledge about which ones are problematic and which aren’t. Here’s what they had to say about their notebook batteries.
I asked: Is it true that keeping your laptop plugged in continuously degrades battery life? GOOG turns up conflicting reports, need authoritative source.
wilw said, “Anecdotally, I can tell you from personal experience that it does. I’ve replaced 2 MBP batteries for that reason.”
kevinmarks said, “it depends on the kind of battery you have in the laptop.”
howtogeek said, “A bunch of good info on the topic“
YourGoToGuy said, “No research. But my Dell battery just went dead after a couple of years for that reason.”
ethnicomm said, “guess it depends on if the battery has *memory* – I thought it was best to run it down to almost nil before recharging.”
cfarivar said, “if so I’m screwed!”
aloncarmel said, “asking the same. Apple answer about Mbp is that it doesn’t harm the batt. I dunno. I still drain it.”
CoreyHarris said, “I have always heard the same thing, But I don’t like to run off battery if I don’t need to.”
room214 said, “I have set my battery to only start charging when below 88% and stop at 99%. It should help increase the life of the battery.”
brandon_wirtz said, “depends on what kind of battery you have. Lead Acid (heavy short life like your car has) Nope. Just LI yes. Li polymer no.”
brandon_wirtz said, “Some Battery types get a memory, some don’t some only charge so many times some don’t”
brandon_wirtz said, “Also depends on if your laptop has a good Voltage regulator for charging. Faster charging laptop is more likely to wear battery”
bonsai said, “With modern LiPoly or Ni-MH batteries, it’s all about the charger rather than batt. chem. so it actually depends on the laptop.”
andrevr said, “Pretty sure that’s not the case anymore. Smart charging circuits and battery tech have kilt that one.”
andrevr said, “Here’s some real data for you to consider. My Air has spent ALOT of it’s life connected.”
FrankRamblings said, “absolutely true. I completely killed a thinkpad battery in 9 months that way. To the point where total batt life was 12 mins.”
scorpusmaximus said, “I’m no expert, but I agree with Ray Maxwell on the battery question. Charging and partial charges degrade them quicker.”
bwhalley said, “it does, for fact. if it’s a desktop that’s portable, only put the battery in when you need to move it.”
alexknight said, “This happens with Lithium Ion batteries. Apple has a kb article that explains you should drain your battery once a month.”
dariomartinezb said, “PLS, share your findings. I keep my laptops connected all the time… I’ve found batt life to be really short for some of them!”
GBendinelli said, “that was true for Nickel Cadmium batteries, but isn’t really true anymore. It’s good to deplete it 100% after every 25 charges.”
davidleary said, “depends on whether or not you Laptop manufacturer is in the Laptop Battery replacement business too”
jtimberman said, “Depends on the battery type. Apple’s info for Macs“
diesh said, “for lithium batteries this is a good heads-up from Apple.”
thompsonpaul said, “recommendation is to remove battery when under AC power for long periods.”
thompsonpaul said, “Yup, it’s true, at least for Lithium Ion, as stated in ASUS’s laptop usage guidelines. Will try to find you online src”
thompsonpaul said, “Worst condition is keeping charged batt @ elevated temperatures, which is case w/ running laptop batts. http://cli.gs/BrvPnY“
revtristy said, “It’s true for me. I kept my laptop plugged in most of the time and now my battery shuts off randomly when not plugged in. Sad!”
ChrisKubica said, “If u have a Mac, this app helps u see info re yer battery’s life. A pic“
chrisbarber86 said, “Yeah it does, ideally you need to either remove the battery, or charge it up full, run it down 99% flat, then charge again etc”
tchachra said, “I have a laptop at home on my desk always plugged in. Never had a battery issue. Mac’s and or PC’s.”
haselhurst said, “i believe this is true. my battery was fine, then left laptop plugged in continuously for 2 years, no buggered.”
Cocodmonkey said, “experience says yes.”
GitEmSteveDave said, “I pull the batteries out of mine occasionally.”
emilsit said, “My bet? Depends how smart your charger is (and what battery technology).”
gdarklighter said, “no. Modern power supplies are smart.”
biggsjm said, “According to Apple you need to cycle once a month. Run down to empty and then recharge.”
joshbrez said, “My first MBP battery ran down enough w/ it always plugged in for Apple to replace it for me”
UnreadZigmund said, “I’ve also researched this after buying a netbook but couldn’t see a consensus.”
sameersama said, “well as far as personal experience is concerned then it does mess up the battery.”
puneetsarda said, “yes it does My laptop’s battery life has fallen to 35-40mins”
robert_wheeler said, “from experience supporting many laptops yes leaving them plugged in degrades battery life but it can take months to happen”
jaskirat said, “No way. Using your laptop on battery all the time degrades battery!”
guscuddy said, “I’m no expert, but my last laptop battery died after a little over a year (and all of a sudden) because I kept it plugged in.”
emhs said, “At the Shack, we have a policy to not keep the battery in demo laptops. Not quite authoritative, but close.”
Update: This Bit About Batteries (see the “Calendar Life” section) explains details of Li-Ion battery life under different conditions. Thanks @ChrisKubica!
Of course, the best way to find out is to RTFM for your notebook and battery type to be sure,. My primary notebook is a MacBook Pro, and as per Apple’s suggestion, I don’t keep it plugged in continuously at my desk. (Because I’m on my second battery already, I’m paranoid and pull the plug a couple times a week.) Image courtesy of andrevr.
I usually just charge my laptop over night, and carry it around in sleep mode all day in my backpack. Run it down during class, charge it back up at night.
As far as I know (From Wikipedia/li-ion batteries), temperature is much more important to battery life. So just unplug the battery (if possible) when you know you are not going to use it for some time.
Or throw it in the refrigerator plugged in for extended periods.
I found this website to be a pretty thorough resource on all things battery.
The correct answer is: Yes, leaving your laptop plugged-in all the time will kill the battery. There is no definitive study that I can point to, but every article I’ve ever read concluded it to be true, and the overwhelming majority of anecdotal evidence from users of all brands report this to be the case.
The best solution, however, is not to unplug. If you unplug, discharge, and plug back in, you’re adding unnecessary cycles. The best thing to do is to remove the battery when you’re not actively charging it, and stay plugged-in. (This is possible with all laptops, except for the newer MacBooks.)
Also, just to echo what Kasper said, batteries are sensitive to heat. That’s another reason not to leave your battery attached while it’s not in use, as the internals of laptops get pretty hot (100-150 degrees is typical), and batteries do best at room-temp (70 degrees) or cooler.
Wikipedia (the references, actually) has decent info. To summarize (hopefully, I’ve remembered everything correctly):
* For modern lithium-ion batteries, heat is likely to be the #1 cause of shortened laptop battery life (being next to high-temperature laptop parts is not really good). Heat is a killer; generally, the cooler the battery is kept (but not freezing or below), the longer the useful battery life.
* Lithium-ion batteries like short discharge/charge cycles. Deep discharges aren’t good for the battery.
* However, the battery meter circuitry does generally need a periodic deep discharge for calibration purposes (so that your battery meter reads correctly). Yes, this is at odds at “deep discharges” aren’t good for the battery, but this is an engineering tradeoff: do you want an accurate battery meter or not? In theory, doing it once a month shouldn’t affect the useful lifetime appreciably, which is why the vendors recommend that a deep discharge be done once a month or so.
* Lithium-ion batteries don’t have memory.
* Generally, lithium-ion batteries start degrading from the moment they’re made (due to oxidation, IIRC). Because of this, it may not make sense to buy a spare (to use when the current battery degrades).
* Long-term storage should be with a partial, and not a full charge.
Also, in case it’s not obvious: keeping the laptop plugged in and turned on all the time, keeps the battery warm/hot, which shortens the battery life. If you must keep the laptop plugged in all the time, turn off/suspend/hibernate the laptop.
Look no further than my mac for proof (though more than one data point is usually recommended). Info from the CoconutBattery app:
Battery-Load Cycles: 91
Age of your Mac: 36 months
Original Battery Capacity: 5500 mAh
Current Battery Capacity: 1764 mAh (32%)
As a point of comparison with Claudio, I regularly unplug my MBP and use my battery down to the reserve power warning before plugging back in. her are my CoconutBattery stats:
Battery-Load Cycles: 695
Age of your Mac: 19 months
Original Battery Capacity: 5600 mAh
Current Battery Capacity: 2433 mAh (43%)
So what does tell us? My battery is half as old as Claudio’s but I cycle it far more frequently. I have more life left in it but should it have more being newer, or less due to heavy cycling?
I keep my 14-month-old MacBook Pro plugged-in practically 24/7. Now it shuts down without warning at 60% charge (it doesn’t even go to sleep, it just dies) and the battery icon says “Service Battery.”
There’s a chance it’s not related to keeping the laptop plugged-in all the time, but once I replace the battery I won’t be doing it any more.
I have this Lenovo 3000-Y500 for about 4 years now and it hasn’t shown much decline in battery prowess.
I just make sure its plugged in only when it is on or has less charge.
I unplug it when not in use and full battery.
a mod on thinkpads.com forums suggested i let my 9cell drop to ~40%, then recharge. when on the dock i wait til it drops to 99 or 98%, then unplug, drain to 40% or so, then recharge. after 4 years of ownership and one battery, i’ve still got near full capacity. seems like a good tip for this type of battery.
My work laptops have always been continually charged since they are in a docking station all day – I work in a cube and connect 2 monitors, mouse, keyboard. as a result, my battery life eventually dwindles to about 15 minutes which turns my laptop into a workstation.
Any rechargeable battery, in my experience, must be used pretty regularly or they won’t hold a decent charge. This is true of all the double-A’s I own, my 14.4v Makita, and my laptops. I try to get my laptop battery down to 10% or so at least once a month.
I have 3 HP laptops at home that are always plugged in except for the occasional trip out of the house. 2 are used for 6-10 hours a day. The third is turned on and used about once every 10 days and used for about an hour. They all have 6 cell batteries, all 18 to 24 months old. Using advice I received from an HP level 2 tech, I leave the batteries out all the time (when plugged in) and only insert the batteries once a month, at which time I switch to battery power and run them all down to 2%, and then fully recharge them. All 3 of the batteries are still running at 80 to 85 percent of their ‘new’ capacity, based on how long the machine actually runs before neeeding recharging. This compares with my previous HP laptops’ batteries that were left in the laptops all the time and were essentially useless by the time they were 24 months old. Just my 2 cents worth on my personal experience.