Some factors 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 what it feels like when 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.
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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.
It turns out that the single most important way to maximize battery life is something 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 the output voltage of the charger can have a 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 to less than 100 cycles.
While I suspect things have improved since this article was first written in 2006, especially with the adoption of the USB-C power standard, I had no idea that batteries could be that sensitive.
I purchase batteries, extra batteries, and chargers from the manufacturer when I buy a laptop. That further minimizes any manufacturing differences that may occur over time.
The #2 factor in battery life? Temperature.
The fact is that laptops just aren’t designed 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 any flat surface you might put it on. That creates important space for ventilation. If you block that space — say with your lap — you’ll cause the laptop to run hotter than it should. If you do this regularly, you’ll 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 provide a flat or even grooved surface (for even more space and airflow) on which to comfortably place your laptop.
Temperature cycling — allowing the laptop to become cold and then warm repeatedly, say by regularly leaving it in your car overnight in cold weather — can also adversely impact the battery’s life.
Leaving it plugged in
A concern I’ve had for a long time is whether or not leaving a laptop plugged in for extended periods 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, as my laptop is plugged in and running pretty much 24×7.
“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.
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