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Is there a program (preferably free) made for testing the battery life of a laptop? That would sort of... keep the time, prevent it from going into standby, etc. Maybe have one mode where it just keeps the laptop alive, and one where it does lots of computations and keeps it very active as well.

How do various magazines and websites test this?

I know there are manual ways of doing this like putting on a movie and set it to repeat, but then I would have to watch it until it died to take the time, etc. Would like a "standardized" automated test of some sort.

My platform is currently Windows 7, but something that works in Vista and XP (and maybe even Linux distros like Ubuntu) would be very nice, so that I could run the same test and compare.

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3 Answers 3

up vote 4 down vote accepted

Did a quick Google search and found a few things:

Battery eater pro is a free app that should give some better battery stats: http://www.benchmarkhq.ru/english.html?/bepro_e.html

This CNET article also talks a bit about how they test notebooks: http://reviews.cnet.com/Labs/4520-6603_7-5142378-1.html

If you're running Mac OS X, the detailed system information provides information on the number of charge cycles, the estimated percentage of battery remaining (at a full charge) and other details.

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The OS X tool is called "System Profiler" in your Applications->Utilities folder. –  Dave K May 20 '09 at 22:36

There's two ways of benchmarking batteries: filling it to full and timing how long it takes to fail, and trusting/verifying what ACPI report.

I suspect you're asking for the former. What you might do is grab a clock, turn off battery settings and let it drain under some workload. When it fails, stop the clock and there you go.

GNOME does the latter, you can bring it up under battery properties. They keep a record of ACPI reported charge and battery life and the rate at which this changes during discharge time. What you end up with is a good prediction of history in the middle, with less confidence of the prediction at the end because you don't often run a laptop to dead, and when you do, disk writes become dicey. The end near 100 percent decline is also unreliable, for reasons I'll explain next.

One caveat to modern laptop batteries: their performance degrades over time. My laptop battery that lasted 4 hours when new lasts 30 minutes at best now. I'd be interested to see anyone who has data on how a battery declines over time and use. Every time your battery charges to full, it goes to a slightly lower voltage / capacity, and that's why you don't have good confidence at the top end; you visit it every time you unplug and every time is different.

But let me caution you against the drain-to-failure approach. What you really care about is how it will perform in some future situation. Will you be able to watch two movies on your flight? Or take notes in this meeting, etc. In that situation, you don't care about the extra 1 percent you might get by skipping hibernate at critical battery life; you care about the integrity of your work. Just take the system off AC, do your job, let it hibernate when it normally would and check the clock.

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batteryuniversity.com has exhaustive information on battery performance. See e.g. batteryuniversity.com/parttwo-34.htm for charts on capacity loss of lithium-ion batteries. –  sleske Jul 13 '09 at 18:29

You could write a little script that writes the current time&date to a file once a minute or so.

In Bash, it would be something like:

while true; do date; sleep 60; done >/tmp/datelog.txt

On Windows, you could probably do it with a BAT (or install Cygwin ;-)).

Start that, then let the computer run until it shuts down. Then you can look at the logfile to see how long it ran.

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This approach could lose the last 5 minutes of disk activity due to write-caching on the hdd. Also, on some machines, the /tmp/ directory isn't persistent. This is highly dependant on how your system is set up, but I'd stick the results in your home directory just to be safe. Still +1'd for a good, if slightly flawed idea. –  Babu Jul 13 '09 at 20:06
    
Was actually thinking about, and almost starting, to create a program that did that in C# or something. Looked into some stuff on how to prevent a computer from going into stand-by etc as well. Shouldn't be too difficult actually... Just have to find the time... =/ –  Svish Jul 13 '09 at 22:08

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