Some are more sensitive than you might think
I originally wanted to title this article “Why does my battery life suck?”, because I know that’s exactly what it feels like when the battery life gets shorter and shorter. My oldest laptop has about a 20 minute lifespan, so in many ways the battery is really nothing more than a glorified UPS. Not that that’s bad, but it does limit the laptop’s portability.
Some years ago I turned to a friend, the late Jerry Foutz, for some help on this one. Jerry’s site, SMPS Technology (via archive.org), was a canonical reference for power supply design.
Become a Patron of Ask Leo! and go ad-free!
Maximizing battery life
- Get chargers that match, as exactly as possible.
- Don’t let the computer and battery overheat.
- Leaving it plugged in all the time is no longer the issue it once was.
Match making
It turns out that the single, most important aspect to maximizing battery life is something that I wouldn’t have thought of: matching the battery to its charger. In Jerry’s words:
“Make sure your battery and charger match and you have a quality charger. About the only way you can maximize the probability of this happening is to buy both from the computer manufacturer for the exact computer model.”
Apparently even small differences in output voltage of the charger can have dramatic impact on the lifespan of your battery, by either under, or over-charging.
“If you get a low-cost charger and it is off by as little as 10 mV (millivolts, 1/1000 of a volt), you will also get less than optimum performance.”
An example Jerry shared is that a 4.1V cell charged at 4.050 V might be good for 4,000 charge cycles. Increasing the charge voltage to 4.250, a difference of less than 1/4 of a volt, can reduce this down to less than 100 cycles.
While I suspect things have likely improved in the intervening years, especially with the adoption of the USB-C power standard, I had no idea that batteries could be that sensitive.
I’m also glad that I’ve purchased my batteries, extra batteries, and chargers from the manufacturer at the time I got my laptop. That, further, minimizes any manufacturing differences that may occur over time.
Running hot
The number two factor in battery life? Temperature.
The fact is that laptops just aren’t designed for … well, for laps. If you look at the bottom of your laptop you’ll see it probably has feet (or more likely, bumps or rubber pads) that lift it off of any flat surface you might put it on. That creates very important space for ventilation. If you block that space, with say your lap, it’s likely that you’ll be causing the laptop to run hotter than it should. If you do this regularly, you’ll likely shorten the lifespan of the laptop’s batteries.
Again, in Jerry’s words:
“If you have your laptop on your lap and it is burning you, you are shorting the battery life and charge-cycle capability because you have interfered with its cooling system.”
If you do like to use your laptop on your lap, there are various “laptop desks” out there that will provide you a flat, or even grooved surface (for even more space and air flow) on which to comfortably place your laptop.
Temperature cycling – allowing the laptop to become very cold and then warm, repeatedly — say by leaving it in your car overnight in cold weather regularly can also adversely impact the battery’s life.
Leaving it plugged in
A concern that I’ve had for a long time is whether or not leaving a laptop plugged in for extended periods of time would harm the battery. Today’s designs pretty much expect that type of usage, so it’s not the issue I was afraid it might be. Good thing, too … my laptop is plugged in and running pretty much 24×7.
Finally:
“All this assumes a well designed power supply (including charger and battery). Unfortunately, not all designs are perfect and the layman has almost no way to judge the quality of the design. You pretty much have to trust the manufacturer and his reputation.”
Thanks again to Jerrold Foutz for contributing to this article.
Hi Leo,
Two important things that I did not mention when we talked about batteries are aging and storage.
Lithium-ion batteries start to deteriorate from the day they are manufactured. The mechanism is an increase in internal resistance. For a spare battery the ideal storage conditions are at a 40% charge at 0C (32F). In practice, store it in the refrigerator (not freezer) in a sealed bag after you discharge it to 40% of capacity as measured with the fuel gauge in your laptop. At these ideal conditions, the battery will still have 98% of its capacity after a year storage. But store it with a 100% charge and it is reduced to 94%. If you store it just above room temperature at 25C (77F) with 100% charge you drop to 80%. This is the way I stored my spare before I knew better. This capacity loss is non-recoverable. The capacity is gone forever. If your computer is always on and in use, the battery temperature may sit in an environment of 30C (86F) and drop to 65% capacity in a year. If it reaches 40C (140F) you can drop to 60% capacity in only three months! You get the idea why keeping your battery cool is so important. From the battery perspective, removing the battery while on AC power would reduce its temperature and help battery life, but from a power supply designer’s perspective, this is not recommended. The presence of the battery provides substantial design margin to your laptop as well as protecting it from power surges and sags.
The increased internal resistance has an additional effect besides increasing internal battery temperature when current is drawn. When there is a current surge caused by hard-drive access or heavy CPU usage, the surge of current working against the age-increased internal resistance can drop the terminal voltage so that the protection circuits trigger and won’t let you use it. There is still capacity, but you can’t get to it in an aged battery.
An excellent website on batteries for your readers is the Battery University. This is the source of the percentages I quote above.
Jerrold Foutz
> If you have your laptop on your lap and it is burning you, you are shorting the battery life and charge-cycle capability because you have interfered with its cooling system.
To say nothing of your own libido and fertility, if you happen to be male!
Take care, Leo!
-cw
is there a software to keep ur battery charged for a considerably longer time????
I see replacement batteries that say they will match my laptop but they have higher voltage. For instance, my battery says DC10.8v and 400 mAh. Replacement that says it will work for me is 11.1 and 450. I do not use an external charger, jsut recharge within my laptop…
Great article, Leo (with appreciation from Jerrod, of course)! I just ordered a new Dell Inspiron E1505, and I’ll take the advice given on this page to heart. Thanks, guys!
I purcahsed this refurbished HP DV5224NR laptop on boxing day 2006 from futureshop. I have two problems with it. The short battery life and the used up harddrive space.
The battery life lasts a maximum of 1.5 hours – 2 hours under regular usage of surfing the internet and maybe listning to music at the same time. I have noticed that roughly every 1 minute, a percentage of battery is used up.
Secondly, the avaliable harddrive space to use when first opening the computer is approximately 50 GB. The 30 GB that is used up is the 12 GB taken up in the recovery partition and the rest in the programs that come pre-installed from HP.
These are my two cons, if anyone has the same peevs, please share.
Otherwise, so far the laptop is going well.
Can zinc-air cells (hearing aid) be recharged? How do I extend their life?
I have a Hp Pavilion and my battery have never lasted longer than 15 minuts. I paid $1,300.00 for my computer. I bought it from Best Buy. What happened?
-Leo
Try to avoid leaving the charger in the laptop when the battery is at 100%. This overcharges. If you know you’re using mains and the battery is at 100%, slide the battery out! The laptop still works.
I’ve read articles about the upcoming electric vehicles that will use lithium-ion batteries, similar to what is in laptops. These articles say that the auto industry is struggling with the problem that whenever the charge in lithium-ion batteries goes below 40% the life of the batteries is reduced. Therefore, I assume the same is true in laptops.
I like your article that guide me to increase the battery life of laptop. Mobile computing has got better with lighter components, better chips and faster processor. To get rid of this we should, we have to follow these point that are Reduce your monitor brightness, Do one thing at a time, Shut down services you don’t need and Keep it cool. Thanks a lot .
I have a cochlear implant for my hearing. I have four batteries which have to be charged daily i.e one every four days (they are used one at a time, not together). These batteries are still going strong after four years. What a shame laptop batteries are not made of the same stuff. Mind you they are £100 each
A more practical comment would address the consequences of overcharging by leaving the charger connected beyond full charge. Why don’t charges automatically shut down when they recognize a fully charged battery ?
How can you know for how long to charge a battery?
01-May-2012