How It Works: Batteries

by Dustin Sklavos

"How it Works" has been going strong for eight chapters now, and here in the ninth chapter we get to a subject that frankly, I've been dreading: batteries. This is a situation where explaining how the battery itself works is largely irrelevant; instead, it's more important to know how to choose a battery, how to save battery life, and how the battery itself decays.

There are problems here. While I can be credibly marked down for missing one or two points of minutiae in the last article, when talking about batteries there's a mountain of hearsay. Even more than the urban legends that surround them, there are other factors that ultimately make them difficult to talk about. Lenovo, for example, regularly squeezes obscene amounts of battery life out of their laptops, while an Asus equipped with the same hardware will get borderline half as much battery life. I can't give you the precise reason why.

So here we go, getting into Part IX of "How it Works" and talking about one of the most important and misunderstood parts of your laptop: the battery.

How It Works: Batteries

Before I get into the nitty gritty of this, I need to make something clear: I'm neither chemist nor engineer, so the nitty gritty details and minutiae of batteries are things I won't go into. This is largely because understanding them isn't really relevant to understanding how to care for and use your laptop battery.

First and probably most important is that Metallica lied to you: battery is not, in fact, here to stay. Lithium Ion batteries (commonly referred to as LiIon) have been powering laptops for quite some time now, and if anything in this world is ephemeral, surely these are. These batteries begin losing capacity - not charge, but full capacity - from the moment they come off the manufacturing line. That means that your battery life is going to be at its best the day you buy your laptop and from then on, it will become progressively worse. Period.

That said, laptop batteries have to be pretty impressive given the fact that they power an entire computer. And mercifully, compared to other parts like processors or graphics cards, battery statistics are incredibly easy to understand. There are really just two statistics to them: number of cells and life rated in milliampere-hours (mAh). There is, however, no way to totally gauge how much battery life a computer can pull from these. An ASUS Eee PC 1000H netbook, for example, can pull a staggering six hours out of a six cell battery. By the same token, I had an old ASUS laptop that, at the time I bought it, would be lucky to hit 2:30 from the same-sized battery. So as I mentioned before, there are variables here, and I'll discuss them.

Cells and Power Hours

Laptop batteries are comprised of groups of cells. Traditionally, low capacity batteries contain three to four cells; the average laptop battery is a six cell. When you get into 17" laptops, batteries tend to contain eight or nine cells. Finally, I've seen high capacity batteries go up to twelve.

What's important to understand is that the number of cells the battery contains directly affects the size of the battery itself. In smaller laptops (12.1" and under), for example, going beyond three or four cells often results in a battery that hangs out the back of the notebook. Likewise, the 12-cell high capacity battery HP offers for their 14.1" and 15.4" laptop lines (they're kind enough to at least standardize the battery) lifts up the machine, tilting it up on a flat surface and having the pleasant side effect of producing a more comfortable typing angle (depending on who you ask).

3-cell standard battery on HP 2133 Mini-Note

6-cell extended life battery on HP 2133 Mini-Note

The battery itself will also be rated for either watt hours or more commonly, milliampere-hours, or mAh, and again, more is better. Where this gets a little bit tricky is that some batteries are able to produce a smidge more milliampere-hours out of the same number of cells using higher capacity cells. I've seen six cell batteries offer just 4400 mAh, or go up to 4800 mAh or better.

Battery Life

Here I'm going to explain about the easiest things you can do to improve battery life in your laptop, and it amazes me how many users aren't familiar with some of these. This isn't even going to get into the nitty gritty of the control panels, really, they're just basic tips.

First and foremost, the most power hungry component of your laptop by a long mile is the screen. While LED-backlit screens (see Part VIII) do draw substantially less power than CCFL-backlit screens, they still draw a decent amount of power. Fortunately, laptop manufacturers are aware of this and gave you a way to dim the backlight, thus improving battery life greatly. Backlight brightness is generally controlled by a combination of the Fn key on the keyboard and a pair of the function keys, which dim or brighten the screen depending on which you press. By dimming the screen while running on the battery to where you can comfortably read it, you can potentially add at least a half hour to your useful battery life if not more.

The second thing you can do is disable your wireless connection. Laptops always include some way of toggling the wireless card on and off, usually with a dedicated switch but occasionally with the tried and true Fn and function key combination. While this is something you may be loathe to disable and is becoming less and less relevant as newer wireless cards draw less and less power, it's still worth knowing. If your laptop is Bluetooth-enabled, disable that when you're not using Bluetooth to avoid wasting power.

Third is what you use your laptop for. Frankly, gaming on the battery is a good way to kill it in a hurry. Modern 3D games tend to be very hardware intensive. Pushing your CPU and video hardware at full bore or near full bore is going to draw more power, but this only gets magnified by the heat they generate as a result, which pushes the fan in your laptop that much harder as well. If you're just playing Solitaire or Minesweeper you don't have a lot to worry about, but if you're trying to play World of Warcraft or Doom 3 during class, your battery is likely to go in a hurry.

In this vein, doing heavy Photoshop or video work isn't going to thrill your laptop's battery a whole lot either. While it's not the kind of killer that gaming can be, it still pushes the processor pretty hard, causing it to draw more power as a result. And finally, playing DVDs or Blu-rays on the battery is also a good way to kill it, though at least laptops tend to be semi-optimized for this. These tasks draw more power by virtue of having to spin up the optical drive, and in the case of Blu-ray can pretty aggressively tax both the CPU and video hardware.

Given all this information, you can probably assume installing software on the battery from a disc isn't going to do you any favors either.

So what the hell can you do? Well, remember, you CAN do any of these tasks, you just need to understand they're going to hit the battery a little harder and make peace with that.

Shopping for Battery Life

While I do plan on putting together a full bore "buying a laptop online" guide at a later date, for now I can give you some key pointers on how to shop for a laptop that can maximize the useful life out of its battery.

As far as screens go, LED-backlit screens make a big difference in power draw and can improve your battery life while also producing a much more pleasing picture. It also bears keeping in mind that if you buy a larger laptop, it's going to have a larger screen, and that larger screen is going to need more power.

Dedicated graphics hardware (remember Part V) is always going to take a bigger bite out of your battery life. If you must have the absolute best battery life you can, you're better off with integrated graphics.

As of the time of this writing and likely for the foreseeable future, Intel processors generally produce superior battery life than AMD's do. It's a hard fact of life, especially for those of us AMD stalwarts. Intel's P series mobile processors seem to be the cream of the crop right now, sitting in a mainstream segment and reporting a TDP of 10W less than T series processors. Oftentimes, thin and light and ultraportable laptops will contain low voltage or ultra low voltage processors, and these are going to do the best on battery life but come at a premium cost.

If you're slumming it and hitting low cost laptops, you're likely just not going to get the battery life you want. These tend to use cheaper and fewer cells in the batteries to get the cost that low and pass the savings on to you, so to speak.

And finally, look at the review of the laptop you're eyeballing. Notebook Review has reviews for an alarming number of laptops on the market, and better, there's probably at least one person on the forums who owns the laptop you're looking at and can answer questions about it for you.

Your Battery Is Not Here To Stay

And now we come to the hard fact of laptop batteries: they lose capacity over time. First of all, anyone who tells you not to constantly recharge it, or to power cycle it, or whatever, is cracked out. Power cycling it may calibrate software in the battery that tells the computer how much life the battery has left, but that's it. LiIon batteries begin losing capacity the instant they come off the conveyor belt, period.

The one thing these batteries are sensitive to is temperature. If you're planning not to use a battery for a while, keeping it in the freezer will substantially reduce the steady loss of capacity. The site Battery University has a little more math (okay, a lot more) for you to dig on here, but basically you'll want to reduce the battery to about a 40% charge and then freeze it, and that will help reduce the loss of capacity.

Unfortunately, you probably want to use your battery. That means that the increased temperatures that come with running your laptop are going to take their toll on the battery's capacity.

Given regular, average use coupled with the math on Battery University's site, it's safe to assume your maximum battery life will be reduced by roughly a third by the end of the first year.

One important thing to keep in mind is that contrary to what anyone says, laptop LiIon batteries do not have a "memory" the way other rechargeables might. This is not how these batteries lose capacity.

And finally, do not buy a battery and plan to use it later. As I said, batteries lose their charge the instant they come off the line, so avoid buying the battery until you intend to use it.

Conclusion

Yet another article where I can't really give you any recommendations. That's because ... hey ... these are batteries. Part of the problem is that there's no real good metric for measuring how much battery life you can expect from a laptop because of the design decisions each manufacturer makes. I can say that I've generally seen solid battery life out of HP's hardware, and I've heard good things about Dell's. Lenovo is practically a class leader here. Likewise, though I love ASUS, their laptops tend to have mediocre to poor battery life. As the stalwarts on the forums will tell you, an ASUS laptop just wouldn't be an ASUS without some kind of horrible fatal flaw, and nine times out of ten, that battery life is it.

As for the steady decay of battery life, well, it comes with the territory. The nice thing about bigger, high capacity batteries is that even though age sets in, their useful life is longer as a result of just holding more. I have a nearly two year old 12-cell HP battery powering my HP Pavilion dv2500t that still gets me about four useful hours on the charge.

Oh, and those of you that are wondering where the section on battery recalls is, there's a simple answer: there isn't one. Recalls occur for all kinds of stuff, though admittedly laptop batteries seem to be a little more prone. But that's a business and manufacturing detail.

And that concludes Part IX of "How it Works." At this point, if you can't practically build your own laptop there may be no hope for you, but fear not ... we'll get it all covered.

Coming Up: Networking

Because I hate myself, we're gonna talk about ethernet and why I'm prone to calling wireless networking "wireless notworking." Stay tuned!

 

nice! as far as I am concerned the best one yet.

PS: T500 + 100%screen + balanced = 5.5-6hours!

 

Pulp,

Thanks for your continuing contributions to this great community. Great work as usual, and I really like the way some of your past articles are tying into this one. Thanks again for your frank and informative writing!

 

What about lithium polymers? Some manufacturers recently started shipping their products with polymer batteries - such as ThinkPad X300 - but only few know about them in details.
Are there any other advantages from them other than the lower profile, and how differently they need to be treated?

 

Keep it up m8,really nice job

 

Great article Pulp. Loving the series.

 

I give you much credit for writing this, especially since you are not an engineer.

This topic is really something that should be covered by an engineer, as I'm sure you know. There are a few critical flaws in your article which I must point out, but let it be clear that you deserve a lot of respect for writing this. You obviously spent a lot of time doing research.

I do feel a strong need to criticize these statements:

First, batteries really only have one important "statistic". That is the (milli)watt-hour rating. This is the true capacity of the battery and the one statistic that affects battery life.

If you want to get technical, you could say that batteries have two important statistics: (milli)amp-hours and voltage. I will do my best to leave as much engineering and math out ot this. My simple explanation is that amp-hours and voltage together affect/determine watt-hours. The number, type, and specifications of the individual cells determines amp-hours and voltage(which together determine watt-hours and thus battery life).

Here is where equations become necessary if you wish to further understand how all this works. Watt-hours is the product of amp-hours and voltage. So a higher amp-hour battery will not necessary last longer or be any better as your state in your article. A 19volt 3600mAh battery will last much longer than a 7.4volt 5400mAh battery when both laptops use energy at the same rate. In fact, the 3600mAh battery will last more than one and a half times as long as the 5400mAh battery.

It is quite possible to calculate exact(or at least, very close to actual) battery life given the power draw on your laptop(watts) and all the given specs on the battery if you know all the necessary equations. Just putting that out there. Batteries aren't magical energy sources that last some random period of time.

 

Great one, I would refer people to this link if they have any general questions about batteries.

 

Add some more pictures.

 

Thanks again pulp for another excellent guide. Also, thanks to JPZ for going into the details.

And that is exactly how your notebook's battery timer works. It is based on the total Whr remaining divided by the power drain (in W) at that certain point in time. That is also why the time remaining flucturates as the power drain changes when you for example open up Windows Mediaplayer which increases the GPU load and therefore increasing the power drain.

 

Nice article . I'd just like to point out that in the link you posted, they say NOT to freeze your batteries for prolonged storage, but just to keep them cool.

 

What about using your battery for the very first time? A lot of companies recommend charging for about 12 hours on the first charge when you use your new laptop. Why is this?

 

This is a great guide!

Thanks!

Cin

 

Excellent article ... Many thanks!

 

I felt the article was not of any help.It hardly carries any useful information for a new laptop buyer.I know u would not like to get technical but the regular visitors of the forum expect a bit more.You havent mentioned anything about lithium polymer batteries.And then you go on to mention how lenovo in general has very good battery life.How can u make a general statement like that.
1,The lenovo series derived from the thinkpad line (like to X series) ,Apple macbooks and sony vaios use lithium polymer batteries which give them a very good power to weight ratios.Polymer batteries according to my experience also hold the power better during power discharge cycles.I have also noticed that lithium polymer batteries have better battery life for MAH though reputes sites like batteryuniversity will tell you otherwise.
2,The other advantage of polymer batteries are that they can be moulded onto various shapes and fit non even surfaces(which is why the mac air is so thin)
3,Battery life depends also on the system used.The new atom processor sips energy at 3-5 watts TDP.The new 1066 mhz buses on the penryn processor use memory voltages of only around 1.8 volts.This also brings down energy consumption.
4,Not to forget battery life also depends on the OS used.Generally windows XP will give you 10-15 % more battery life than Vista.However this seems to have been reversed in Windows 7.Mac OS X will generally give you 25 % more battery life than similarily configured windows machines.......

 

I appreciate anyone willing to play devil's advocate and say "no, actually, this is a useless article."

That said, your logic is flawed. Calling me out for making a generalized statement about ThinkPad battery life and then making generalized statements like #4 in particular harms your credibility. In the instances of some laptops, the power management software is going to be better optimized in Vista than in XP.

I do agree the omission of Lithium Polymer batteries is probably an important one, but their market presence is rarefied compared to the vastly more common Lithium Ion.

Finally, I'd like to think my article is useful if for no other reason than to at least provide tips on saving battery life. While some of this may seem obvious to you, my experience with other less-informed users has involved actually showing them how to dim the screen and explaining to them why they would do so.

 

Excellent article, yet again Pulp!

(You seemed a bit stressed in your writing )

 

The article misstates that you should place your battery in the freezer for storage when not in use to prolong the battery life. This is incorrect... you should store it in the refrigerator. This comes from batteryuniversity.com